A. Only if the water level in the coastal areas rises, then the people change their lifestyle.
B. People change their lifestyle only if they are rewarded.
C. If people are rewarded, then they will not change their lifestyle.
D. If the temperature rises, then the water level in the coastal areas rises.
E. Whenever the water level in the coastal area rises, then the temperature rises.
F. Unless the people change their lifestyle, temperature rises.
G. People are rewarded.
H. Water level in the coastal areas does not rise.

Let us solve the problem by eliminating the options.
G: People are rewarded
C: if people are rewarded then they will not change their lifestyle.
F: Unless people change their lifestyle, temperature rises This can also be put In the following manner.
If people do not change their lifestyle then temperature rises.
This is an example of binary logic - If not A then B which can also be expressed as if not B then 'A'.
Thus if the temperature doesn't rise then people change their lifestyle.
Here, accordingtoG and C, people do not change their lifestyle and so temperature rises.
D: If temperature rises, then water level in the coastal area rises.
H: Water level In the coastal area doesn't rise.
Here, D is in accordance with G, C and F but H is not So option (A) is incorrect.
B: People change their lifestyle only if they are rewarded.
This means that if people have changed their lifestyle then they have been rewarded.
Note that if people are rewarded, they may or may not have changed their lifestyle.
G: People are rewarded.
From B and G. we don't know whether people have changed their lifestyle or not.
F: Unless the people change their lifestyle, temperature rises.
This can also be put as - If the people don't change their lifestyle then temperature rises
But

as we don't know whether people have changed their lifestyle or not,

v/e cannot conclude whether temperature has risen or not.
D: if temperature rises, then water level in the coastal area rises.
H: Water level in the coastal area doesn't rise.
As we don’t know whether temperature has risen or not, H cannot be concluded using D.
Hence, option (B) is also incorrect.