一些英语的问题!1.We should take active part in the action of ( )ani

一些英语的问题!
1.We should take active part in the action of ( )animals.
A.protect B.to protecting C.protected D.to protect
2.There is no difference between the two words.I really don't know ( )
A.to choose which B.which to choose
C.to choose what D.what to choose
3.We found ( )necessary ( ) protect the environment.
A.it ; to B.this ; of
C.that; to D./ ; of
4.Many people decide ( ) the animals in danger.
A.not to kill B.not to killing
C.don't kill D.to not kill