问题详情

What does the professor say about discontinuous permafrost？
A．It is subcategorized as either extensive or sporadic.
B．It is an early indicator of periods of global warming or glaciation.
C．It covers approximately 24% of Earth"s land area.
D．It is the most common form. of permafrost.请帮忙给出正确答案和分析，谢谢！