风湿性心脏病并发充血性心衰的诱因包括( )。A．风湿活动 B．感染 C．过度劳累

多项式a²-c²+ab-bc分解因式的结果是______．

As one of the most popular artists in the US, not only_______ with her hit songs, but has inspired women with her devotion to charity.

A．has Beyonce influenced pop culture

B．influenced pop culture has Beyonce

C．Beyonce has influenced pop culture

D．influenced pop culture Beyonce has

机械物件通常的裂缝探测方法有（）等。

A.渗透探伤法

B.磁粉法

C.电阻法

D.超声波探伤法

E.渦流法

既是我国地势第二级与第三级阶梯的分界，又是省级行政单位分界线的山脉是（）

A.大兴安岭

B.阴山

C.太行山

D.昆仑山

图书馆学与相关学科存在着几种类型的关系？