---I ________ this morning，but he could not come．

---Well，we'd better go and _________ at his office．

A.called him；call on himB.called on him；call himC.called at him；callD.called him；call at him在线课程A
解析：
call可表示“给……打电话”，根据会话的语境，第一空应填 called him；
call on sb．表示“拜访某人”，是固定搭配.答案为A.