DNA was found to contain only four different chemical building blocks.
Answer:
I believe it's an organ
Explanation:
Organs have atleast two or more tissue types and preform specific sets of functions for the body.
Answer:
1. Essential organs form during early development
Explanation:
Harmful chemicals (toxins) cause the most disease when they are present during fetal development, because organ systems are being developed and the rate of growth is very fast.