The krebs cycle takes place within the:
a. mitochondria
b. lysosome
c. vacuole
d. cytoplasm

The Krebs cycle occurs in the mitochondrial matrix (mitochondria) and generates a pool of chemical energy (ATP, NADH, and FADH2) from the oxidation of pyruvate, the end product of glycolysis. 
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Both (A) and (B)

Explanation:

Relative humidity usually refers to the quantity of water vapor that is present in the air in order to get saturated at the same given temperature. It is expressed in terms of percentage (%).

This relative humidity can be primarily changed in two different ways, such as-

(A) By changing the air temperature- Temperature is an important factor here, as by increasing or decreasing the air temperature, the relative humidity can be altered.

(B) By changing the amount of water vapor present in the air- The amount of water vapor that air can store gradually increases with the rise in temperature. So the warm air contains more moisture content in comparison to the cold air, thereby having high relative humidity.

Thus, both (A) and (B) are the correct answers.