15. (A) He needs help to retrieve his files. (C) He needs some time to polish his paper. (B) He has to type his paper once more. (D) He will be away for a two-week conference.

18. (A) New laws are yet to be made to reduce pollutant release. (B) Pollution has attracted little attention from the public. (C) The quality of air will surely change for the better. (D) It’ll take years to bring air pollution under control.