Contour lines that are close together indicate a slope than lines that have more separation between them.

The statement is correct.

The contour lines are a very good indicator of the relief. The closer they are to one another, the steeper the relief, and vice verse, the more distant they are from one another, the flatter the relief is.

In general, contour lines that are very close to each other can be noticed on the mountains, as most of the mountains have steep parts, or rather steeper slopes.

The more distant contour lines, on the other hand, can be found on places like the valleys or the plateaus, places that in general are much flatter.

d.) greenhouse gases