Last year he learned ________ he had expected because he worked a lot harder.

题目考查倍数表达法，根据题干中的信息“Last year he learned ________ he had expected because he worked a lot harder”，可知是倍数的比较级表达。选项A中的“twice as much as”是倍数表达法的第二种结构，表示“是……的两倍”。而“学到的东西”是不可数的，所以用much来修饰，因此答案为A。