Why are there no aircraft or spacecraft flying or orbiting in the mesosphere? A. Aircraft are not powerful to reach the mesosphere and spacecraft can't orbit that low.

B. There is danger of meteor strikes in this layer.

C. Spacecraft would burn up at orbital speeds and it's too thin for aircraft wings to achieve lift.

D. The ionized gases in the mesosphere prevent radio contact with aircraft and spacecraft.

Use the drop-down menu to match the following definitions to the corresponding terms. the total variety of organisms that live in the biosphere a group of organisms that breed and produce offspring that can breed all of the biotic and abiotic factors in an area

What are the fixed alleles in the human species? o a. the alleles that are on the most chromosomes b. the alleles that change most often 000 c. the alleles that no one has d. the alleles that everyone has

In an experiment examining the effects tai chi on arthritis pain, callahan (2010) selected a large sample of individuals with doctor-diagnosed arthritis. half of the participants immediately began a tai chi course and the other half (the control group) waited 8 weeks before beginning. at the end of 8 weeks, the individuals who had experienced tai chi had less arthritis pain that those who had not participated in the course.