In Terms of Long- Term Temperature Increases in the Atmosphere

In terms of long- term temperature increases in the atmosphere, which of the following is TRUE?

A) It appears that we can readily curb the carbon dioxide problem.
B) The greenhouse effect has never been shown to be real.
C) Increases in greenhouse gases have been observed.
D) Average global temperature has risen 5.0°C this century.
E) No changes have been observed in this century.