They will fly to Washington, ______ they plan to stay for two or three days.

A．where

B．there

C．which

D．when

( )是采用与管道材质相同的板材用模具冲压成半块环形弯头，然后组对焊接而成。

A．冲压无缝弯头
B．冲压焊接弯头
C．焊接弯头
D．高压弯头