Identify $A, B$ and $C$ in the given diagram.

$A$ - The salt concentration is less than $5$ (parts per thousand) in inland waters.
$R$ - The salt concentration is $30 - 35$ (parts per thousand) in the sea.

What is the basis of variations in the physical and chemical conditions of different habitats?

Consider the following statements $(A - D)$ each with one or two blanks.
$(A)$ Some snails go into $ . . . . . . (i) . . . . . . $ to avoid $ . . . . . . (ii) . . . . . . $ related problems.
$(B)$ Since small animals have a $ . . . . . . (iii) . . . . . . $ surface area relative to their volume,they tend to lose body heat $ . . . . . . (iv) . . . . . . $ when it is cold outside.
$(C)$ Next to temperature,$ . . . . . . (v) . . . . . . $ is the most ecologically important environmental factor.
$(D)$ Every $ . . . . . . (vi) . . . . . . $ the famous Keoladeo National Park in Rajasthan hosts thousands of migrating birds.
Which one of the following options gives the correct fill-ups for the respective blank numbers from $(i)$ to $(vi)$ in the statements?

The temperature gradient over the Earth's surface is:

Plants of salty seashore wetlands are called