During top coal caving mining, the essential cause of top coal crushing is ( ).
A: softening of water in roof strata
B: the stress it beared is large than its own strength
C: the gas in the top coal expands, leading to breakage
D: cracks produced by raw coal during its formation
A: softening of water in roof strata
B: the stress it beared is large than its own strength
C: the gas in the top coal expands, leading to breakage
D: cracks produced by raw coal during its formation
B
举一反三
- Which of the following is not a common way for coal caving? ( ) A: Top caving coal in group sequence B: Top caving coal in single cycle sequence C: Top caving coal in multiple cycles in sequence D: Top caving coal in intervals of single cycle
- While it has set targets to increase its consumption of ( ), China remains the world’s top producer and consumer of coal
- Rich in coal, abundant in oil and gas, while coal is the most important basic energy and raw material in China.
- Quantity of energy contained in the atmosphere is ______. A: smaller than that in coal alone B: smaller than that either in oil or in gas that we have on Earth C: greater than that in coal, oil and gas on Earth combined D: greater than that in coal, oil and gas on Earth, respectively
- What are the main disadvantages of fully mechanized caving technology? ( ) A: More coal loss B: Fire prone C: Big coal dust D: Gas is easy to accumulate
内容
- 0
Softening Claims” Using natural gas instead of coal ______ prevent air pollution”
- 1
The most easily oxidized coal is (). A: lignite coal B: bituminous coal C: lean coal D: anthracite coal
- 2
_____________ is the process of extracting coal from the ground. A: Overfishing B: Overconsumption C: Coal mining D: Burning of fossil energy sources
- 3
Coal can be converted （） gas by burning
- 4
In terms of equivalent calorific value, the lowest price among coal, oil, natural gas and renewable energy is ( ). A: oil B: coal C: renewable energy D: natural gas