问题
选择题
While every possible means __________ to prevent the river pollution, the river in my hometown has still not been restored to its past beauty.
A．is tried
B．are tried
C．has been tried
D．have been tried
答案
C
题目分析：句意：尽管阻止河流污染的每一种可能的办法都已采用了，但我家乡的河流仍没能恢复到以前的美丽。means单复数同形，但句中means前有every修饰，故谓语动词要用单数，由句意可知应用现在完成时。
考点: 考查动词时态和语态及主谓一致的用法。