Which of the following is the best example of gene flow? a) an earthquake kills most individuals in a tree population, leaving just a few survivors. b) wind blows pollen from one population of plants to another, and cross-fertilization occurs. c) genes are shuffled by the crossing over of chromosomes during meiosis. d) a polyploid plant develops.

explanation:

b,bacteria convert nitrates

into nitrogen gas.

d,plants and animals take in

and use nitrogen compounds.

e,bacteria break down waste    

products and return nitrogen  

to the soil.

a,bacteria convert atmospheric

nitrogen to ammonia.

c,bacteria convert ammonia

to nitrites and nitrates.

answer: 21

step-by-step explanation:

divide 630 by 30. 30 goes into 630 21 times

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.

it's not c. i took the quiz and got it wrong. so my best guess is b.

have a great day, and hope this .