Understanding the Sentence Completion Question

The question asks us to complete a sentence about NASA's exploration of Mars, specifically focusing on what its exploration aims to find.

The incomplete sentence is: "NASA’s exploration of Mars ___________________ that may have existed, and relate it to finding evidence of ancient life."

We need to choose the option that correctly fills the blank, maintaining grammatical accuracy and logical flow.

Analyzing the Subject and Verb Agreement

The subject of the sentence is "NASA's exploration of Mars". The main noun here is "exploration", which is singular. Therefore, the verb that follows must also be singular.

Evaluating Verb Tense and Form

The sentence discusses NASA's ongoing efforts and their relevance to finding ancient life. The present perfect tense (has/have + past participle) is often used to describe an action that started in the past but has a connection or continuing relevance to the present. Given the context of ongoing exploration and linking findings to current goals, the present perfect tense seems appropriate.

Furthermore, the phrase "focused on" is typically followed by a gerund (the -ing form of a verb acting as a noun) or a noun. So, "focused on finding" is the correct structure.

Checking Noun Agreement

The sentence mentions finding "traces and trails of water". Both "traces" and "trails" are plural nouns, suggesting evidence of multiple instances or paths of water. The forms used in the options should reflect this plurality.

Examining the Options

Let's look at each option based on our analysis:

• Option 1:

  have focused on finding traces and trails of water

This option uses "have focused". Since the subject "exploration" is singular, the singular verb "has" is required. So, this option is incorrect due to subject-verb agreement.

• Option 2:

  has focused on finding traces and trails of water

This option uses "has focused". "Has" agrees with the singular subject "exploration". It uses the correct structure "focused on finding" (gerund). It also uses the correct plural nouns "traces" and "trails". This option seems grammatically correct and fits the context.

• Option 3:

  has focused on find traces and trails of water

This option uses "has focused on find". The verb form after "focused on" should be a gerund ("finding"), not the base form ("find"). So, this option is incorrect.

• Option 4:

  has focused on finding traces and trail of water

This option uses "has focused on finding" which is grammatically correct in structure and tense. However, it uses "trail" instead of "trails". The sentence structure implies multiple traces and trails. So, this option is likely incorrect due to noun number disagreement.

• Option 5:

  focused on finding traces and trails of water

This option uses the simple past tense "focused". While grammatically possible in some contexts, the present perfect "has focused" better conveys the idea of a focus that began in the past and continues to be relevant to ongoing goals (relating it to finding ancient life). Compared to Option 2, Option 2 is a better fit for the context of NASA's current focus and its relation to finding ancient life.

Conclusion

Based on the grammatical rules of subject-verb agreement, verb forms following "focused on", appropriate tense for ongoing relevance, and noun plurality, Option 2 correctly completes the sentence.

The completed sentence is: "NASA’s exploration of Mars has focused on finding traces and trails of water that may have existed, and relate it to finding evidence of ancient life."