She thinks swimming is so difficult to learn that she wants

首先确定本题考查意图.显然,四个选项是动词,即本题考查动词的词义辨析.
其次还原原句,是句子更加清晰,即she thinks 后面是一个宾语从句,只不过that常常省略,还原后是She thinks 【that】 swimming is so difficult to learn that she wants to ___ it.,宾语从句为swimming is so difficult to learn that she wants to ___ it.此外,本宾语从句中又有一个固定搭配,so.that.表示“如此,以至于”
最后,可知句意为“她觉得游泳太难了,以至于想放弃学习游泳”,drop有“丢下”“放弃”的意思.A是丢东西的意思,C是跌倒的意思D是忘记.显然B最符合题意.