A scientist wants to test the effect of water temperature on the success of developing frog embryos. The scientist monitors developing embryos in different water temperatures and counts the number of embryos that mature into tadpoles.

Why should the scientist keep all variables except water temperature constant?

A to test multiple variables at once
B to ensure at least some embryos develop into tadpoles
C to ensure that the results only reflect changing temperature
D to protect the developing embryos

chemical weathering

explanation:

the element that provides strength to the exoskeletons of clams and oysters is phosphorus. this is so because calcium carbonate is the main component in the shells.

explanation:

stimulus is a change in the environment that causes an organism to react. the response is the reaction to the stimulus. some examples of stimuli for zebras are drought, to many predators, and bad feeding grounds such as dead grass or plants. zebras respond to stimuli just like all other living organisms

the last one: artificial selection/genetic engineering

plant breeding is modifying the genetic composition of the plant - but this isn't cloning (which is specifically introducing a gene into a genome). but you are artificially selecting for the phenotype that you want.

the second one is literally genetic engineering - the gene would have been cloned first and then inserted or genetically engineered into the new plant cell (the cotton).