______ his timely help, Kate overcame the hardship at last.                                                                                                                                                                                                                                                                                                                                                                                                                         

A．Now that

B．Thanks to

C．Since

D．Because

车间内的低、中压乙炔管道都应选用壁厚小于3.5mm的（）管。

A.无缝钢管

B.焊接钢管

C.螺旋钢管

D.铜管