What controls the menstrual cycle? at what age does the menstrual cycle begin (approximately)? what age does the menstrual cycle end (approximately)? are there things that one can do to manipulate the cycle into not occurring? be very elaborate

the answer is a or when it says crossing over

the backbone of the dna and rna compound is sugar phosphate.

thrombocytopenia, which is a deficiency in blood platelets, can cause bleeding and bruising in the dermis similar to senile purpura. other possible causes include: exposure to ultraviolet rays and aging skin are common causes of senile purpura. senile purpura may also be a sign of collagen loss in the skin and bones.

oxygen = 21% of the atmosphere

nitrogen = 78%

carbon dioxide = 0.1%

argon =0.934%