Why are stomata only located on the underside of leaves?

Question

Why are stomata only located on the underside of leaves?

Answer 1

In most plants the stomata are located on the underside of the leaves.  Their function is regulated so that plants living in dry climates have a substantially smaller number of them than those in humid climates, where they are numerous and prominent.  Where humidity is low the stomata may actually be recessed or partly protected by soft hairs which can prevent excessive transpiration.

Answer 2

They aren't.  Most dicots are hypostomatic -- stomata mostly on the underside of the leaf; monocots are typically amphistomatic (both sides).  Some of the floating leaf aquatic plants (among others) have stomata on the upper leaf surface (epistomatic).

Answer 3

I believe this is because if they were on the upper side of the leaf, they would come into direct contact with sunlight, causing the plant to lose of water from evapotranspiration.

Curious because the question was on this year's GCSE unit 3 biology paper?