Mark the letter A, B, C or D to indicate the underlined part that needs correction in each of the following questions.
Question 29: She has disappeared three days ago, and they are still looking for her now.
A. has disappeared B. and C. are still D. for her
Question 30: Ozone has his origin in a number of sources, a prime one being the automobile engine.
A. his B. prime C. being D. the
Question 31: After going through a protection period that may last from several months to a year, new recruits will be offered a long-term contract.
A. going through. B. protection. C. last. D. new recruits
