Question

When investors purchase a commodity, they believe

Answer 1

A. The commodity's price will go up after purchase.
They hope that at some point they will make money on their purchase.

Answer 2

When investors purchase a commodity, they believe - the commodity's price will go up after purchase.

The investors invest certain amount on a commodity, and believe that it's price will increase so as to benefit them. This is not guaranteed though but the investors believe in this because this is the only way they will make profit out of their purchase.