During an el nino, warm water piles off of south america and cold water can't upwell. as a result, the can't rise and so small organisms have no food source.

The correct answer is - nutrients.

The cold water is very rich in nutrients, and those nutrients are crucial for the survival of the small organisms as they are their primary food source. When El Nino occurs though, the water is becoming warmer and stops the up-welling of  the cold water, which also means that the nutrients remain deep with it. As a result, the small organisms are left without their primary food sources, thus they struggle to survive, and even die out in the region on a large scale.

the answer is c.) there is a warm front in region a and a stationary front in region b.

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.