It took me quite a long time to develop a voice, and _______ I have it, I am not going to be silent.

A．now that

B．unless

C．so that

D．although

冷气机用的管子大多数是利用（）管，此管分硬质和软质二种，再各分二种厚度，K和L，K型管较（）适用于（）的地方，L型管是供（）用途。