nservation area is very important for preservingmany animals and plants, which would ______ run the risk of becoming extinct

Who ________ a theory about black holes

Does your new secretary ____ shorthand

well-known to us all that knowledgeis __ treasure, but practice is ___ key to it.

依次填入下列各句横线处的成语，最恰当的一组是（ ）①如果敌人进攻山区，民兵就在每一座山头上 ；如果敌人进攻平原地区，民兵就打地道战。②这支英雄舰队， ，日夜守卫在东海前哨。③除此之外，团队中的每个成员，无论是经验丰富的“老兵”，还是年轻的“新兵”，都必须 ，随时准备奔赴赛场。