The introductory modifier describes the entity doing the reviewing, which logically is "the product team." The other choices are illogical or ambiguous: an app or a tutorial cannot draw such conclusions, and "they" lacks a clear antecedent.

"Their" agrees in number with the plural antecedent "many prospective students." "His or her" is singular, "its" is singular and refers to a nonperson, and "it's" is an incorrect contraction.

Because the subject is the singular phrase "a series," the correct verb is "is." The other choices either mismatch the singular subject ("are," "have been") or use an illogical tense with a scheduled future event ("were").

After 'recommended that,' Standard English requires the base form of the verb ('revise') in the subjunctive mood. The other choices use incorrect agreement or tense/aspect for this construction.

The head noun 'The number' is singular, so the verb should be 'has remained.' The other options use plural agreement or inappropriate tense/aspect for a condition persisting over time.

By the time signals that the leak's damage occurred before another past action, so the past perfect had damaged is required. The other tenses do not clearly establish the earlier time frame.

With 'neither...nor,' the verb agrees with the nearer subject 'supervisor,' which is singular, so 'is' is correct. The other choices mismatch number or tense.

The introductory modifier must describe what was recorded only once, which is 'this rare sighting'; it also sensibly serves as the subject that 'suggests.' The other choices create illogical or unclear references for the modifier.

The time marker 'before' calls for the past perfect progressive 'had been' to show an ongoing action completed prior to another past event. The other options either use the wrong tense/aspect or do not reflect the earlier ongoing action.

With 'neither...nor,' the verb agrees with the noun closest to it; 'producers' is plural, so 'were' is needed. The other options use singular agreement or the wrong tense/aspect.