Question

which is a requirement for natural selection to occur?
heritable variations for some traits
the ability of an organism to improve a trait during its lifetime
equal probability of survival for all offspring
fewer offspring than the environment can support

Explanation:

Natural selection requires heritable variations in traits. These variations allow some individuals to have a better - chance of survival and reproduction. Lamarckian idea of an organism improving a trait during its lifetime is not a requirement. All offspring do not have an equal survival probability in natural selection, and there are usually more offspring than the environment can support, not fewer.

Answer:

heritable variations for some traits