Carbon dioxide and oxygen are important resources in ecosystems and are; (a)recycled through the activity of living and nonliving systems b) stored in the animals of the ecosystem c) lost due to the activities of decomposers d) released by the process of photosynthesis

The correct answer is (A)recycled through the activity of living and nonliving systems.

Carbon dioxide and oxygen are important resources of any ecosystem. Oxygen is essential for all living beings as it is required in cellular respiration (aerobic) while carbon dioxide is used as a source of carbon in plants for producing sugar and other essential nutrients.

In an ecosystem, resources including oxygen and carbn dioxide are recycled through the activity of both living and non-living systems.

For example, carbon dioxide is used by plants (living) and is released by living system such respiration of animals and plants and decaying of dead animals and plants . In addition, it is also released by non-living system such as burning of fossil fuels, biomass combustion, volcanic eruptions etc. In this way carbon dioxide keeps cycling in an ecosystem.

Similarly, oxygen is also cycled with the help of living and non-living systems. For example, it is released in atmosphere as a byproduct of photosynthesis and is used by all living organisms. Non-living system such as photolysis of water also helps in release of some amount of oxygen in an atmosphere.

"menstrual cycle is a complex cycle that consists of several processes. order of occurrence of steps in menstrual cycle are as follows:

1. high progesterone levels maintain the endometrium lining of the uterus.

2. endometrium lining breaks down and low levels of estrogen stimulate the pituitary to release fsh and lh.

3. fsh and lh stimulates the follicles to develop and the oocyte to produce estrogen.

4. rising estrogen levels suppress fsh production and development of other follicles.

5. a spike in lh causes follicle to rupture.

6. a breakdown of corpus luteum causes progesterone level to drop."

genetic variation can be caused by mutation (which can create entirely new alleles in a population), random mating, random fertilization, and recombination between homologous chromosomes during meiosis (which reshuffles alleles within an organism's offspring).