【正确答案】 D

【答案解析】本句的意思是：我刚刚要离开办公室，电话铃响了。be about后面接不定式，表示“刚刚要……”。再如：I was about to jump over the small ditch when I fell over a stone．我刚要跳过一个小水沟，突然摔倒了。“be+to do'’与be abou t to do的意思完全一样，要注意区别，如：He was about to lock the door when he suddenly remembered that he had left the key on his desk．他刚要锁门，突然记起把钥匙忘在桌子上了。The president is to visit five African countries．总统计划访问非洲五国。