入团积极分子要进行不少于（）个课时的集中培训时间。*

A、6个

B、7个

C、8个

D、9个

Aluminum lifeboats are subject to damage by electrolytic corrosion (the aluminum being eaten away). In working around boats of aluminum you must be very careful（）.

A.to keep the boats covered at all times

B.not to leave steel or iron tools lying in or near these boats

C.to keep an electric charge on the hull at all times

D.to rinse these boats regularly with salt water