Ecotourism is one of the most rapidly growing form of specialized travel in the West，with central American countries，such as Costa Rica，________the principal destinations at present．
A.be B.to be C.being D.been正确答案C
Ecotourism is one of the most rapidly growing form of specialized travel in the West，with central American countries，such as Costa Rica，________the principal destinations at present．
A.be B.to be C.being D.been正确答案C
