简述血吸虫疫苗的研究的3各阶段。

A. only the sternlight of the vessel
B. a sidelight and one masthead light of the vessel
C. only a sidelight of the vessel
D. any lights except the masthead lights of the vessel

A. 行车安全
B. 加固安全
C. 设备安全
D. 机械安全