It is only by practising English for several hours every day _________ be able to use it freely.

A．will you

B．may you

C．that you will

D．when you must

我国煤矿生产安全状况较差的原因较多，但煤矿职工整体素质较差，法律意识淡薄是不可忽视的主观因素。