What option best fills the gap labelled 6

The passage below has gaps. Immediately after each gap, four options are provided. Choose the most appropriate option for each gap. 

In modern mining, there is a network of __6__ [A. way B. tunnels C. paths D. avenues] and passages, with openings and walls which in the dim light seem very bewildering. Right across the wall at the end of the inky black passage, the __7__ [A. miners B. toilers C. workers D. foreman] approach. The coal __8__ [A. front B. slope C. obstacle D. face] is neatly cut __9__ [A. slit B. gash C. bare D. aperture]. It extends level to a height of rather less than three feet. The rays of the miner’s lamp shine on steel roof __10__ [A. beams B. supports C. spurs D. stays]. Thousands of feet of rock and earth are pressing down on those steel plates and __11__ [A. props B. wedges C. poles D. stakes], and the miners have to crawl through the small, deep opening in the wall to get to the coal in the mine that we are considering, the __12__ [A. gash B. hole C. seam D. opening] is nearly four feet thick and is being worked by a combination of __13__ [A. digging B. manpower C. machinery D. spade] and explosives. A mechanical __14__ [A. slit B. gash C. knife D. mesh] saws into the coal to a depth of four or five feet, thus separating it from its base. Explosives pushed into holes drilled at intervals in the coal are __15__ [A. fused B. extinguished C. detonated D. stuck] by remote control and blow the separated section of the coal to pieces.