How do you know that the steadfast tin soldier,by hans christen andersen, was set in the past?

The setting. they have muskets,castels ect

The answer is B. The students did the experiment in the lab on Wednesday. To make it not passive, the sentence needs to be changed so that the students are the active ones in the sentence. All the other options make the experiment the passive thing being "done", whereas in B, the students are the ones " doing " something.