下面属于聚酯类可降解材料的是
A. 聚3-羟基烷酸酯
B. 聚ε-己内酯
C. 聚磷酸酯
D. 聚乙交酯
聚磷腈主链结构是由磷和氧原子交替组成的高分子聚合物
A. 对
B. 错
Manual workers often receive much higher ______ than people who work in offices
A. gains
B. fees
C. payments
D. wages
His ______ kept his secret.
A. brothers
B. workmates
C. companions
D. comrades