With the situation worsening, the army threatens to_______ if a general election is not to be held as scheduled. So let’s _______some serious work.

We visited the museum built __________ those who had died in the war[ ]

ll cost a lot of time ____ , Ithink we shall need it and it will certainly be useful

The doctors and nurses did best to fight Zika Virus(寨卡病毒) in Brazil.

The rivers will become dirtier and dirtier _______ we take action to protect them.