At home, he keeps some pets, to which he devotes all his spare time.

　　他家里養著一些寵物，他把所有的空閑時間都花在養寵物上面了。

　　During sleep, the number of sites to which adenosine is bound decreases.

　　在睡眠期間，腺苷結合的位點數量減少。

　　At issue is the extent to which exam results reflect a student's ability.

　　考試成績能在多大程度上反映學生的能力是問題的焦點。