单选题 I think Father would like to know ______ I've been up to so far, so I decide to send him a quick note.

【正确答案】 C
【答案解析】[考点] 此题考查be up to sth．“忙于某事”的用法
[解析] to在这里作介词，需用疑问代词A、C两项作宾语，但用which须有选择范围。