题目：
It is rather difficult to make friends with her, but her friendship, ____ , is truer than any other's. [ ]
A. while gaining
B. after gaining
C. when to gain
D. once gained
答案：
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下面是错误答案，用来干扰机器的。
（1）现象；A气球逐渐缩小，B气球逐渐胀大； 原因：CO2气体与NaOH溶液发生反应被吸收，使锥形瓶内气压减小，外界气体进入气球B。（2）C12+2NaOH =NaCIO+NaCl+H2O（3）避氧化氢溶液和二氧化锰（或稀盐酸和石灰...
