如图，AB∥CD，∠C=42°，∠E=58°，则∠B的度数为（　　）

如图所示，给电磁铁通电，条形磁铁极弹簧在图中位置静止，当滑动变阻器的滑片向b端滑动时，弹簧长度变短，则螺线管上端为____ （选填“N极”和“S极”），电源左侧为____ （选填“正极”或“负极”），若其其它条件不变，只将电源正负极对调，待弹簧稳定时，弹簧长度与对调前比较将____ （选填“变长”或“变短”）．

A: Good afternoon! How are you?

B: Fine, thank you. Oh, that's Tom speaking.

A: You're right.____

B: Sure,but she is doing her homework. Wait a moment. Lucy, it's Tom.

(After Lucy answers the phone. )

C: Hello. Tom.

A: Hello, Lucy.____

C: I have no idea. How about you?

A: I'm going fishing nearby on Saturday. Would you like to go with me?

C: ____ I'm sure we can have fun together. By the way, How can we get there?

A: ____ It's not far from here.

B: Sounds good. ____

A: Let's make it 8 :00 am at the school gate. OK?

B: OK. See you then.

A: See you.

如图，在△ABC中，AB=BC，BD平分∠ABC．过点D作AB的平行线，过点B作AC的平行线，两平行线相交于点E， BC交DE于点F，连接CE．求证：四边形BECD是矩形．