I hear a number of workers in the factory _____ out of work and the number of them  ______ quite large .   

A． are , is

B．is , are

C．is , is

D．are, are

曲轴箱是柴油机的骨架，它不但支承全部（）机构，而且也是其它许多零部件和机构的装配基础。