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.

the aurora is formed when charged particles emitted from the sun during a solar flare penetrate the earth's magnetic shield and collide with atoms and molecules in our atmosphere. these collisions result in countless little bursts of light, called photons, which make up the aurora.

auroras are generated by charged solar particles hitting molecules in earth's atmosphere. this usually happens in high latitudes, because our planet’s magnetic field tends to funnel these particles toward the poles. that’s why it can be experienced in northern ohio.