Directions: The first and last parts of a sentence are numbered 1 and 6. The rest is split into four parts and labelled: P, Q, R and S. These four parts are not given in their proper order. Read the sentence and find out which of the four combinations is correct.

1. Hydraulic fuel P. which becomes extremely hot during landing, Q. which caused R. had leaked on the 'wheel well area' S. causing smoke and fire
2. the plane to land in an emergency