State health inspectors have demanded that the city authorities

State health inspectors have demanded that the city authorities ________ immediately to clean the water supply.
A、acts
B、acted
C、act
D、have acted
【正确答案】：C
【题目解析】：demand that 从句 为虚拟语气，从句要使用 （should）do sth 形式，句中省略了should 因此选C原形