The answer is solution a must have a lower solute concentration than solution b.
That is when water is moving across a membrane from solution a into solution b, then solution a must have a lower solute concentration than solution b.
When solution a have a lower solute concentration than solution b, then water moves across a membrane from solution a into solution b.
D. All of the above. Developing medicine, analyzing compounds and producing new product such as plastic all have to deal with chemistry.