I used to love science class—all of them— 86.
biology, chemistry, geography, physics.I think I 87.
liked those classes because I felt that it helped me 88.
understand what the world works. For example, when 89.
I was a child, the rain was a mystery(奥秘).In one 90.
class, I learned it rained. I think science classes 91.
clear up mysteries. But then there is always more 92.
mysteries look into. What was my least favourite class? 93.
That was math. After learn the basics of the subject, 94.
nothing else seemed very practically to me. I never 95.
saw how I could use it in my daily life.86.class→classes
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(答案→)86.class→classes
解析：
86.class→classes此题考查名词的数。根据all of them可以确定class要用复数形式。
87.√
88.it→they此题考查代词的用法。they指代classes。
89.what→how此题考查从句的连接词的用法。what在宾语从句中作宾语，而这个句子中的谓语动词works是一个不及物动词，后面不接宾语。
90.去掉rain前的定冠词the此题考查冠词的基本用法。rain在这里是泛指。
91. 在learned和it rained之间加why此题考查从句的连接词的用法。这句话的意思是“我知道了为什么下雨”。
92.is→are此题考查主谓一致。这是一个存在句，在下行中的mysteries可知，要用系动词are。
93.在mysteries和look into中间加to此题考查动词不定式的用法。to look into作mysteries的定语。
94.Learn改为learning此题考查非谓语动词。在介词后要用动名词作宾语。
95.Practically改为practical此题考查形容词的用法。seemed是系动词，后接形容词作表语。