天然橡胶的化学组成是( )。
A.聚酰胺 B.聚碳酸酯 C.聚甲基丙烯酸甲酯 D.聚异戊二烯
参考答案:D
解析:天然橡胶是由异戊二烯互相结合而成的高聚物
In Japan the three _____ means of transportation to get to school are bus, train and bike. [ ]
A. most popular
B. popular
C. more popular
D. popularer
常见前纵隔肿瘤是()
A.胸腺瘤
B.神经源性肿瘤
C.肉瘤
D.平滑肌瘤
E.支气管囊肿