1.(2019·全国卷Ⅰ，62)It is difficult to figure out a global population of polar bears as much of the range has been ________ (poor) studied.
答案：poorly 修饰动词studied应用形容词poor的副词形式poorly。
2．(2018·全国卷Ⅰ，68)To avoid knee pain, you can run on soft surfaces, do exercises to ________ (strength) your leg muscles (肌肉), avoid hills and get good running shoes.
答案：strengthen 在不定式符号to后面用动词原形。
3．(2018·浙江高考，62)The obvious one is money; eating out once or twice a week may be ________ (afford) but doing this most days adds up.
答案：affordable be动词后应接形容词。affordable “付得起的”。
4．(2018·全国卷Ⅰ，43)And, even if I weren't ________ (excite) enough about free credits, news about our instructor was appealing enough to me.
答案：excited 系动词后面应用形容词，此处修饰人，故填excited。
