问题补充：
I must go now. , if you want that book Ill bring it next time.
A. Incidentally
B. Accidentally
C. Occasionally
D. Subsequently
答案：
A. Incidentally
B. Accidentally
C. Occasionally
D. Subsequently
解析：incidentally(=by the way)附带地，顺便：Fred said, incidentally, that he had no dinner.(顺便提一下，福来德那时说，他还没吃晚饭。)accidentally(=by chance)偶然地：I met with an old friend of mine accidentally last week.(上星期我偶然碰到一位老朋友。)occasionally (=from time to time, not regularly)不时地，偶尔：We get visitors here occasionally.(我们偶尔在此接游客。)subsequently(=afterwards, later) At first we thought we would go; but subsequently we learned we were needed at home.(起初,我们想离开；但随后我们得知家里需要我们。)
.
