Lawrence Craven, a doctor from the USA, is the author of _____ several published reports, one of

introduced the idea in 1953 _____ aspirin could reduce the risk of heart attacks. [ ]

A. them; when

B. which; that

C. what; that

D. which; when

能形成防火隔离层并对在火场灭火人员无害，绝热性能好，无毒、有消烟，可排除有毒气体，但不能扑救在无空气的环境中仍然能迅速氧化的强氧化剂和化学物质的火灾的泡沫灭火系统是（）。

A．固定式泡沫灭火系统

B．低倍数泡沫灭火系统

C．中倍数泡沫灭火系统

D．高倍数泡沫灭火系统