A. Children who have private music tutors. B. Children who are 8 or older. C. Children who are between 5 and 7. D. Children who are well-educated. 参考答案:B 答案解析:有关细节内容的测试题。可从文中“very young school children aged between 5and7 showed no bias in choosing musical ins
第30题: [单项选择]龈下牙石是 A. 沉积于龈缘以上牙面的牙石 B. 沉积于牙周袋内根面上的牙石 C. 肉眼可见,呈浅黄色 D. 形成较快,质地较松的牙石 E. 用器械较易去除的牙石 参考答案:B 答案解析:位于龈缘之下、附着于牙周袋内根面上的牙石称为龈下牙石,肉眼见不到,需用探针才能查到。质地坚硬,相对于龈上牙石则附着紧密,较难去除。