【答案解析】credible：可信的。convincing：可信的。That is the least convincing excuse that you could offer. convincing可替换credible而不改变句子的意思。workable：可行的，行得通的。
Your plan is workable. practical：实际的，现实的。He is weak in practical matters. reliable：靠得住的。John is a reliable man.