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 correct answer is - d. china has a large and growing population.

the fact that china has a large (the biggest) population, and it is still growing, doesn't hinder the agriculture production in the country. in fact, it can for increased production in the agriculture, since there's more labor force, as well the sheer mass of people produces lots of scientists that come up with new inventions as to how to improve this sector. nice example is the inner mongolia region in china, in general dominated by the gobi desert, but few scientist came up with a nice idea as to how to make the region productive by using plants that are very resistant to droughts, so lots of people have been employed, and the region is becoming greener and greener each year, and the production of food in this region is also increasing.