Official Solution:If a certain job started in August and ended in September of the same year, did it take more than 30 days to complete? (1) The job started on August 25.
If the job ended on September 1, it took less than 30 days. However, if it ended on September 30, it took more than 30 days. Not sufficient.
(2) The job ended on September 20.
If the job started on August 31, it took less than 30 days. However, if it started on August 1, it took more than 30 days. Not sufficient.
(1)+(2) We know the exact dates of start and finish, and thus can answer the question. Sufficient.
Answer: C