单选题 He was proud of being chosen to participate in the game and he ______ us that he would try as hard as possible.

【正确答案】 D

【答案解析】insure意为“保证，确保”；guarantee意为“保证，担保”；assume意为“假设，臆断”；assure意为“向……保证，使放心”，通常构成assure somebody that结构，意思是“向……人保证”。根据后面的us that可知，应选assure。