公安机关各警种间的分工与协作是各警种正确履行职责所不可或缺的条件。但是警种的没置并不是一成不变的，它必须随着形势的发展和公安工作的需要，作相应的调整，增设新警种，淘汰不适合形势的警种。( )

It is usually warm in my hometown in March, but it _____ be rather cold sometimes.[ ]

A. must

B. can

C. should

D. would