Understanding the Sentence and Verb Tense

The original sentence is: "Which movie have you watched on television when I called you?"

This sentence describes an event that happened in the past ("when I called you"). The question asks about an action ("watching a movie") that was likely in progress at the specific moment the call occurred.

The underlined phrase, "have you watched," uses the present perfect tense. The present perfect tense is used to describe an action that happened at an unspecified time in the past, or an action that started in the past and continues to the present, or an action that happened recently with a present result. It is not typically used to describe an action that was ongoing at a specific point in the past when another action interrupted it.

The phrase "when I called you" indicates a specific point in the past. We need a tense that describes an action happening at that specific past time.

Analyzing the Substitution Options for Verb Tense

Let's look at the options provided to substitute the underlined segment:

1. are you watching
2. No substitution required
3. were you watching
4. did you watched

Evaluation of Each Option:

• Option 1: are you watching

  This uses the present continuous tense. The present continuous is used for actions happening now, at the moment of speaking, or for future plans. Since the sentence talks about something that happened "when I called you" (in the past), the present continuous tense is incorrect here.

• Option 2: No substitution required

  As discussed earlier, "have you watched" (present perfect) is not the appropriate tense to describe an action ongoing at a specific past point in time ("when I called you"). Therefore, substitution is required.

• Option 3: were you watching

  This uses the past continuous tense (were + verb + -ing). The past continuous tense is used to describe an action that was in progress at a particular point in the past. The structure "when I called you" provides that specific past point in time. Asking "What were you watching?" describes the activity that was ongoing at the moment of the call (the interruption). This fits the context of the sentence perfectly.

• Option 4: did you watched

  This option attempts to use the simple past tense ("did... watched"). However, the structure itself is grammatically incorrect. The simple past question form for "watch" is "Did you watch...?" The auxiliary verb "did" is followed by the base form of the main verb, not the past tense form. Even if it were "did you watch," the simple past tense asks about a completed action in the past. While "Did you watch a movie?" is correct grammar, "What did you watch when I called you?" would imply watching the *entire* movie or finishing watching it around the time of the call, which isn't the primary meaning conveyed by the interaction where one action (calling) interrupts or happens during another (watching). The past continuous ("were you watching") specifically focuses on the ongoing nature of the action at that moment.

Why 'were you watching' is the Correct Choice

The sentence asks about an activity that was likely happening at the specific moment a past event (the call) occurred. The structure "What were you watching when I called you?" correctly uses the past continuous tense ("were you watching") to describe the ongoing action (watching) and the past simple tense ("I called") to describe the interrupting or simultaneous action. This is a standard use of the past continuous tense in conjunction with the past simple tense to show an action in progress interrupted by or co-occurring with another action.

Thus, the most appropriate substitution for "have you watched" is "were you watching".

Revision Table: Understanding Past Tenses

Additional Information on Using Past Tenses

When we talk about two actions in the past, one long and one short, the longer action is often in the past continuous tense and the shorter action (which often interrupts the longer one) is in the past simple tense. The word "when" is commonly used to connect these two parts of the sentence.

• Example: She was studying when the doorbell rang. (Studying was ongoing, ringing interrupted it).
• Example: They were having dinner when the power went out. (Having dinner was ongoing, power going out interrupted it).

In the original sentence, "watching the movie" was the ongoing action, and "calling" was the shorter action that occurred during the watching. Therefore, the past continuous tense is the correct choice for the action of watching.