4. When a star is on the main sequence, it is (1 point) O converting hydrogen into helium through nuclear fusion
O converting uranium into helium through nuclear fusion
O burning hydrogen and oxygen to make heavier elements
burning radiolactive elements to create lighter elements

converting hydrogen into helium through nuclear fusion

Explanation:

Main sequence stars fuse hydrogen atoms to form helium atoms in their cores.

parasites can detrimentally affect their host, but also must not allow their host to die before they can complete their life cycle. some parasites have complex life cycles with many different hosts, and have had to find ways of persisting in many different environments during the change from one host to another. ectoparasites live outside the body of the host, and can more easily  disperse, but are  more exposed to predators, parasites, parasitoids. endoparasites live inside the body of the host, and are therefore protected from the outside environment. but they can be  attacked by the host's immune system. they have therefore developed  mechanisms for dispersal such as  complex life cycles.