Answer:
A : Tissues are made up of various cell types
Explanation:
B : can't be correct because a system is made of many things, so an organ system is made of many organs. As such, it doesn't make sense for organ systems to make up organs.
C : can't be correct because cells make tissues, and tissues make organs, so cells can't be made of organs
D : can't be correct because an organism is the whole living being. Organisms are made of organs, and organs are made of tissues, so tissues can't be made of organisms.
That just leaves A!
