What is the difference between a lake and a pond?

a.
a pond is smaller in size and does not have a temperature gradient.
b.
a pond is smaller in size and has a temperature gradient.
c.
a pond is larger in size and does not have a temperature gradient.
d.
a pond is larger in size and has a temperature gradient.

A) Pond is smaller in size and does not have a temperature gradient.

The pond is smaller in size and a shallow water body as compared to the lake. Sunlight completely penetrates the depth of the pond. This means that the 'Photic zone' ( zone of sunlight ) is present in the whole pond water. Due to this, there is the uniform temperature in the pond water. Thus, no temperature gradient is established in the pond.  

On the contrary, along with the Photic zone, an 'Aphotic zone' ( zone of no sunlight) is also present in lakes. This will result into higher temperature in the upper water and lower temperature in the water beneath it. Due to this, they have a well-established temperature gradient.

Thus statement A) is correct.

where is the scientific experiment?