Identify the true statement. choose one:
a. underground coal mining is dangerous because of possible tunnel collapse and possible methane gas explosions.
b. anthracite coal develops at depth along mountain belt borders, where temperatures reach 600°c.
c. strip mining can be done economically down to a depth of about 1 km.
d. coal began to form on the earth soon after life evolved in the precambrian.

A. Underground coal mining is dangerous because of possible tunnel collapse and possible methane gas explosions.

Explanation:

Dangers of underground coal mining include asphyxiation, methane gas poisoning, tunnel collapse and explosions of methane gas, a highly flammable gas. Methane explosions occur since this gas is a byproduct of coal. This explosion can cause tunnel collapse.

find the surface area of the sphere to the nearest square unit. use a calculator.

a. 254 in.2

b. 64 in.2

c. 127 in.2

d. 1,018 in.2