协同效应
参考答案：
协同效应是指由两种以上的物质相互作用所产生的效果不同于每个物质作用的总和。
主要发生在腮腺，下颌下腺和舌下腺少见，小唾液腺罕见的肿瘤是（）
A．腺样囊性癌
B．黏液表皮样癌
C．多形性低度恶性腺癌
D．腺泡细胞癌
E．沃辛瘤
_____，memories of staying abroad as an exchange student flooded into his mind.
A．Listening to these songs
B．Having listened to these songs
C．He was listening to these songs
D．When he listened to these songs
