Where is light penetration in a river or stream likely to be lowest?

a. the source
b. the mouth
c. the middle portion
d. none of the above

(B) the mouth

Explanation:

"Light penetration in a river or stream is likely to be lowest at the mouth of the river".

This is because in the beginning, the river is basically free of particulate matter and is also clear and so there is an ample amount of light penetration in the beginning.

At the middle portion, the suspended thing is high, but due to the speed of the water, the particles get cleared.

However, at the mouth of the river, there is a large concentration of particulate matter, and thus light penetration is the lowest.

Hence, option B is correct.

the level of progesterone is low at the pre-ovulatory phase of the cycle but it gradually increases and the levels are high at the luteal phase. if pregnancy occurs, the level of progesterone will be high throughout the pregnancy.

if egg is fertilized and the mother gets pregnant, progesterone starts preparing the uterus for the implantation. it starts building up the lining of uterus and make it hostile of the period of pregnancy.