6. Which statement best describes the human respiratory system? A) It is composed of a network of moist passageways that permit air to flow from the external environment to the lungs.
B) Each cell of the human body is in direct contact with the external environment, and gas exchange occurs by diffusion.
C) The external body surface is kept moist to allow for gas exchange.
D) Gases diffuse across membranes on both the external and internal surfaces of the body.

b because they naturally adapt to their environment plz mark brainliest

explanation:

this is true, assuming that the allele is completely recessive and incomplete dominance is not a factor.

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.

im not in connections yet but i might can you some questions. what grade are you in?