Help pls! I think this is biology.

What element is able to combine with itself and hydrogen to form large molecules ?

2. which of the following statements does not accurately describe stem cells? a. embryonic stem cells make up the inner cell mass of a blastocyst. b. with more research, stem cells may be used to repair or replace damaged cells. c. the use of stem cells is without any objections since it can be used in therapies to humans. d. adult stem cells are multipotent and can differentiate into many types of cells.

How long does it take a skateboarder going 6.0 m/s to come to a complete stop if she slows down at a rate of 2.0 m/s^2