"I have a mountain of homework" is an example of an exaggeration used for emphasis.

Here are the answers to the literary knowledge questions:

39. "I have a mountain of homework" is an example of an exaggeration used for emphasis.
The correct option is D.

• Hyperbole is the use of exaggerated statements or claims not meant to be taken literally.

The final answer is $\boxed{\text{D}}$

40. "My grandmother is as blind as a bat" is an example of a comparison using "as".
The correct option is B.

• A simile is a figure of speech involving the comparison of one thing with another thing of a different kind, using "like" or "as".

The final answer is $\boxed{\text{B}}$

41. A character that undergoes little or no inner change in a story is known as a static character.
The correct option is A.

• A static character remains largely the same throughout the story.

The final answer is $\boxed{\text{A}}$

42. "The orange juice is sweet sour" combines two contradictory terms.
The correct option is A.

• An oxymoron is a figure of speech in which apparently contradictory terms appear in conjunction.

The final answer is $\boxed{\text{A}}$

43. A figure of speech in which an unpleasant or offensive object is described in pleasant terms is called a euphemism.
The correct option is C.

• A euphemism is a mild or indirect word or expression substituted for one considered to be too harsh or blunt.

The final answer is $\boxed{\text{C}}$