48.Perseverance is a kind of quality,and that's__it takes to do anything well

答案：A.
翻译：毅力/坚持不懈/不屈不饶是一种品质,它也是做好任何事情所需要的（因素）.
1.此题考查表语从句的引导词.
2.表语从句同宾语从句类似,都属于名词性从句.
如果该从句不缺成分,则用that引导；
如果从句缺少“是否”的疑问,则只用whether引导；
如果该从句缺少其他成分,则选用相应的疑问词加以代替.
3.该题的表语从句it takes to do anything well中,takes后面明显缺少一个宾语,即it takes (what) to do anything well.
它是一个固定句型,即：it take (sb) + sth或some time + to do sth.
（某人）需要某物/多少时间去做某事.
再如：It takes two to make a quarrel.
要两个人才能吵嘴.
It took him three hours to finish the exercises.
他完成这个练习用了三个小时.
4.而D中的why为副词,从句必须确实一个原因状语时才能够使用它来引导表语从句.
如：That's why I was late this morning.
那就是我今早迟到的原因.