It is reported that large amounts of locusts(蝗虫) ______ in their activity in the north now.
A.isB.areC.wasD.were在线课程B
解析：
考察主谓一致。large amounts of locusts大量蝗虫是复数，故谓语动词用复数形式，结合时间状语now可知是表述的现在的状态，故用一般现在时态，选B。