问题
选择题
I had just taken a bite of my hot dog ________ I heard a familiar voice yelling at me from across the crowded school yard.
A．before
B．while
C．since
D．when
答案
答案：D
考察连词。该句为固定句型，sb had just done sth when sb did sth
意为某人刚做完某事，突然……