单项选择题What is the speaker's main topic?[A] Training for a professional athletE.[B] His physical training.[C] How to do cross-country running.[D] How to do mountain climbing.
单项选择题有自然发火可能性的矿井,主要运输巷道应布置在( )内,并采用预防性灌浆或者其他有效的预防自然发火的措施。