The Sulfuric-Acid Clouds on Venus

The sulfuric-acid clouds on Venus:

A) are confined to a narrow layer about 60 km above the planet's surface and cover the whole planet.
B) extend from the surface to a height of 70 km and cover the whole planet.
C) are confined to a layer just above the surface about 1 km thick and completely opaque, rendering the surface invisible from above.
D) are in a layer about 70 km above the planet's surface but are patchy, so the surface can be seen occasionally from above.