基因对性状的控制是通过DNA控制什么物质的合成来实现的？（ ）
A．维生素
B．脂类
C．蛋白质
D．糖类
答案：C
J2-7掣空气制动机工作风缸充气止回阀充气限制堵堵塞后，会使工作风缸压力由零增至480kPa的时问超过（）s。
Questions 27～30
A. It has a tutorial supervision system. B. It has progressive ideas on education. C. Its professors are more interested in research. D. Its staff maintain a good relation with the students.
