Which type of lens can be rotated to select different magnifications?

objective lenses

Explanation:

objective lenses with different magnifications, screwed into a circular "nosepiece" which may be rotated to select the required lens.

any abiotic or biotic factor in an ecosystem that causes a population's size to slow or decrease is a limiting factor.

desert perennials often survive by remaining dormant during dry periods of the year, then springing to life when water becomes available. most annual desert plants germinate only after heavy seasonal rain, then complete their reproductive cycle very quickly.