What process marks the birth of a star? a. a supernova explosion
b. when it begins combining hydrogen to form helium
c. when its mass expands and cools
d. when gravity pulls in nebular dust

What are the responsibilities of the region of the brain highlighted below? =+= will rate brainiest =+=

The vaccine in a flu shot contains weakened flu viruses. how does a flu shot work with the immune system? a. it destroys lymphocytes. b. it destroys macrophages. c. it activates macrophages. d. it activates lymphocytes.

Match the reproductive structures based on their function and the system to which they belong. egg ovary sperm vas deferens vagina fallopian tube testis urethra