Answer:
Question 21: a
Question 22: b
Question 23: either b or c
Step-by-step explanation:
The first two are difficult to explain, but the third can work with b, c, or even d, but since it says 'job' instead of 'jobs' it's most likely either b or c, probably b would sound better but I'm not sure.
PS: Sorry it this isn't that helpful!