Understanding the Sentence and the Substitution

The question asks us to find the most appropriate option to replace the underlined phrase "stands by" in the sentence: "If you are in trouble, Tommy is the friend who stands by you."

The sentence is structured with a conditional clause ("If you are in trouble"), which sets up a potential future situation. The second part of the sentence describes Tommy as the friend who exhibits a certain characteristic or performs a certain action in that situation.

Analyzing the Underlined Phrase: "stands by"

The phrase "stands by" is a phrasal verb meaning to support or remain loyal to someone, especially in a difficult situation. In the original sentence, "stands by you" uses the simple present tense.

While the simple present can describe a general truth or a habitual action, when used in the context of a conditional clause referring to a potential future situation ("If you are in trouble"), the future tense often provides a clearer link between the condition and the resulting action or characteristic.

Evaluating the Substitution Options

Let's look at the given options and see how they fit the context of the sentence:

1. No substitution required: Keeping "stands by" uses the simple present. It implies that Tommy is the type of friend who generally stands by you whenever you are in trouble. This is grammatically possible but might not be the most natural fit for the conditional structure suggesting a future potential event.
2. will stand by: Using "will stand by" employs the future tense. This option connects the potential future trouble ("If you are in trouble") directly with the future action of standing by. It implies that *when* you are in trouble, Tommy *will* be the friend who supports you. This structure is very common and natural in conditional sentences describing a likely outcome or action in a future situation.
3. was standing by: This is the past continuous tense. It refers to an action that was happening at a specific point or over a period in the past. This does not fit the context of the sentence, which is discussing a potential future situation ("If you are in trouble").
4. stood by: This is the simple past tense. It refers to an action that happened in the past. Like the previous option, it does not fit the context of the sentence, which is discussing a potential future situation ("If you are in trouble").

Determining the Most Appropriate Option

Comparing the options, the past tenses are clearly incorrect as the sentence refers to a potential future situation. Between "stands by" (simple present) and "will stand by" (future tense), "will stand by" is the most appropriate substitute because it directly links the potential future condition ("If you are in trouble") to the future action or support Tommy will provide.

Therefore, the sentence "If you are in trouble, Tommy is the friend who will stand by you" flows more naturally and precisely conveys the intended meaning of support in a future difficult situation.

Revision Table

Additional Information: Conditional Sentences and Tense Usage

This sentence is similar in structure to a Type 1 conditional sentence, which typically follows the pattern "If + simple present, ... will + base verb". While the main clause here is "Tommy is the friend who...", the relative clause "who stands by you" or "who will stand by you" describes the friend's characteristic or action in the conditional situation.

Using "will" in the relative clause after a present conditional clause ("If you are...") is a standard way to express a likely future outcome or characteristic in that specific future scenario. It clarifies that the support ("standing by") is expected to occur when the condition ("being in trouble") is met in the future.