What is "effective"?
Work well
What is "spread"?
cover a large area
What is " disease"?
Sickness
What is "immune system"?
the cells and tissues in the body that make it able to protect itself against infection
what is "degree"?
the qualification given to a student after he or she has completed his or her studies
What is "enter"?
get into
What is " play a key role"?
very important