What is a combination of two or more substances in which each substance retains its properties?

Mixture

Explanation:

Mixture -  

It refers to the composition of various substance in random proportion , where the mixture formed may or may not have uniform composition , and the various components does not lose their identity and there is no chemical change observed , is referred to as mixture.

For example ,

The mixture of sand and chalk powder , where both the substances mix together to form a mixture , but still retain their property.

Hence , from the given statement of the question,

The correct term is mixture.

i believe the answer is c. "baking" is the gerund, while "baking blueberry muffins" would be the gerund phrase. hope this ! : )