关于卫生服务的需求和利用研究属于（）
A.调查研究
B.实验研究
C.文献研究
D.健康危险因素评价
E.卫生服务研究
参考答案：E
_____ the front door _____, he had to enter the room through the back door.
A．Seen; painted
B．Seeing; painted
C．Being seen; being painted
D．Seeing; being painted
膜剂中除药物、成膜材料外，常加甘油或山梨醇作
A．避光剂B．抗氧剂C．脱膜剂D．增塑剂E．着色剂
