嵌合抗体是指用（）替换（），保留（）；人源化抗体是指抗体可变区中仅CDR（决定簇互补区）为鼠源，其FR（骨架区）及恒定区均来自人源。

A. You'd better buy a watch.
B. It's three thirty by my watch
Can you see the clock?
D. It's late I think.