C. To show dislike or disappointment through facial expressions
D. A decisively indicative test
Explanation
A litmus test is a phrase that originated from the use of litmus paper in chemistry, which changes color in response to certain conditions.
In a broader sense, a litmus test refers to a situation, event, or factor that clearly indicates whether a particular approach, idea, or decision is effective, valid, or acceptable.
It's a decisive test that provides clear evidence or proof.
