A. The people considered the new law unfair
For a sentence to be written in active voice the subject (in this case the people) have to be the ones DOING the action ( in this case the action is considered). In this sentence you can clearly see that the people are doing to considering
In contrast answer choice B. is passive because the action is being indirectly done. In the sentence it seems like the new law is doing to considering, but we know that it is actually the people
Hopefully this made sense and helped ya!
~Just a girl in love with Shawn Mendes