At last,the police caught him by____arm.A his B the C )

At last,the police caught him by____arm.A his B the C )
At last,the police caught him by____arm.
A his B the C )

At last,the police caught him by____arm.A his B the C )
动词后加by+身体部位表示“抓”
这里表示“抓某人的胳膊将~抓获”
catch sb by the arm 抓住某人的手臂.(固定搭配）