<今日の進捗>
Book8 - 74 (If you were home alone and heard someone creeping around outside your window, what would you do?)

<オリジナル回答>
When you hear other people speaking English, do you sometimes eavesdrop on their conversation? Why?
Yes, when I hear other people speaking English, I sometimes eavesdrop on their conversation because I want to check how much I can understand them.

【解説】
when節は知覚動詞hearを用いた構文になっています。hear O CでOがCするのを耳にするという意味です。