pollute success belong to return to three mean mind

(1) Trees can help protect the environment in many ways，because they are ______ fighters．

(2) The Shenzhou XI spaceship returned to the Earth ______ ．

(3) This beautiful skirt ______ my sister，my mother bought it for her 2 years ago．

(4) Don't give up，even though we have failed twice．Let's have a ______ try．

(5) The ______ of this sentence is not clear to me．