A marathoner's leg muscles often feel heavy and prone to cramping after 20 or more miles. Which of the following is the best explanation for this?
O A marathoner's circulatory and respiratory system cannot take in sufficient oxygen, and the
muscle cells must switch to anaerobic respiration for energy.
O A marathoner's muscle cells contract when glucose reacts with oxygen.
O A marathoner's circulatory system takes in too much oxygen during a race, which causes
muscle cramping.
O A marathoner's muscle cells cannot store glucose for use as energy.

answer >   yes we do, women; have three holes, urethral opening(pee hole, vagina, and the women pee/girls pee out of the urethra like the men do; only they have a single opening to pee/ejaculate.   (sorry if i'm too forward with this, but this is for a biology class, isn't it? )

hope that !         : )

wegner's theory did not explain how the continents could move

explanation:

igneous rocks are formed by solidification of cooled magma (molten rock), with or without crystallization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks.  

the composition depends on the source magma. there are almost a thousand types of composition found till now.  

hope this

essentially, one bacterial cell splits into two daugurer cells. bacterial offspring don't need or get care from their parents because they are in a sense their own parents. that said, some bacteria can and do depend on other bacteria especially in harsh environments such as bacterial microfilms in hot water tanks.