D. He controlled variables by studying one or two traits at a time
The major function of the immune system is to protect the host from environmental agents such as microbes or chemicals, thereby preserving the integrity of the body. This is done by the recognition of self and response to non-self.
Answer:
Hello! The answer should be A
Explanation:
Hope this helps! :) -Jade231234
Explanation:
because at is formed,the lighter part floats on the surface and the really heavy part (like iron and nickel in the core)sank to the middle