1. They didn't feel the least bit frustrated when they were confronted with fantastic difficulties.
2. If we believe something is good and true we should stick to it.
A. hold up
B. keep on
C. hold on
D. keep up
3. The teacher became frustrated when he found that his efforts had produced even less obvious results.
B. proud of himself
4. Air quality is deteriorating fast in our city.
A. being damaged
D. getting worse
5. Three straight lines meeting at three points constitute a triangle.
A. center on
C. consist of
D. come down to