Answer:
Fourth option: 30 days
Explanation:
We three path to complete the project:
Path A:
A1 → A2 → A3
10 days → 8 days → 9 days = 27 days
Path B:
B1 → B2 → B3
2 days → 7 days → 3 days = 12 days
Path C:
C1 → C2 → C3
10 days → 8 days → 12 days = 30 days
Then the duration of the critical path is 30 days, we can't conclude the project until each path has finished