Which of the following statements is true?
A: all the populations in an ecosystem form a community
B: a habitat represents all the biotic factors in an ecosystem
C: The amount of nutrients in soil is an example of a biotic factor
D: Only one population can live in a habitat at a time

A.  all the populations in an ecosystem forma community

Explanation:

answer: the blood-brain barrier is a layer of specialized membranes and cell processes designed to keep undesirable substances from passing from the bloodstream into the precious tissues of the brain. while the blood-brain barrier does keep most bad things out of the central nervous system, it is not impermeable.

explanation:

false because ozone (o3) depletion does not cause global warming, but both of these environmental problems have a common cause: human activities that release pollutants into the atmosphere altering it.

global warming is caused primarily by putting too much carbon dioxide into the atmosphere when coal, oil, and natural gas are burned to generate electricity or to run our cars.

explanation: