They don't feel safe in our town at night because it _____ so dangerous. There's a robbery every week now.[ ]

A. becomes

B. became

C. has become

D. had become

低钙血症时心电图改变是（）。

A.T波正常、Q-T间期延长

B.T波高尖、Q-T间期延长

C.T波低平，出现u波

D.T波低平、S-T段下移

E.异常Q波、S-T段抬高