在C3H9N中N原子以三个单键与其它原子相连接，它具有的同分异构体数目为 （ ）
A．2种
B．3种
C．4种
D．5种
答案：C
正确答案：C
Before loading bulk grain, bilge wells must be covered to（）.
A.add strength to the bilge well strainer
B.permit rapid flow of water to the bilge wells
C.prevent cargo sifting into the bilge wells
D.preven oil, water , or other liquid from reaching the cargo
家刻本的特点有哪些？
