A) Have people worked on Mars? Yes, they have. Has the climate changed? Yes, it has. Have we protected the environment? No, we haven' t. Has pollution destroyed a lot of trees? Yes, it has. Has the world stayed the same? No, it hasn't.
b) 2 have lost
3 hasn't made
4 haven't done
5 hasn't arrived
6have built
7 has changed
8 haven't put