Joke Collection Website - Bulletin headlines - Snow fell on the mountain.

Snow fell on the mountain.

The adverbial of three days in the analysis sentence is an adverbial indicating a period of time, so the tense in the sentence is used in the present perfect tense, and the verb in the sentence is used in the progressive verb; In addition, the subject scientist is the receiver of verb action in the second half of the sentence, so the sentence uses the passive voice, that is, they are all trapped.