Select the option that completes the sentence CORRECTLY. Whilst one group was…

Concept

When two actions happen in the same past time frame, English keeps their tenses in agreement (the sequence-of-tenses rule). If the framing clause is in the past, the action that goes with it in the same narrative is normally in the simple past too — not in the present or the future, which would point to a different time.

Application

The framing clause here is "Whilst one group was busy cooking" — "was" fixes the whole sentence in the past. The blank describes a second action by the other group happening in that same past time, so it must be a finite verb in the simple past:

"Whilst one group was busy cooking, the other collected wood for the campfire."

Contrast with the other forms

• "will collect" is the simple future — it places the action ahead of now, which clashes with the past framing "was busy".

• "is collecting" is the present continuous — it describes an action going on now, again out of step with the past clause.

• "has collected" is the present perfect — it links a past action to the present moment, but here the time is fully past and parallel to "was cooking", so the plain simple past is what fits.

The simple-past form that matches the past time frame is the correct completion.