Task: Question Answering
Input (English): Problem: tough and tricky questions: ratios 4 / 5 of a certain class left on a field trip. 1 / 3 of the students who stayed behind did not want to go on the field trip ( all the others did want to go ). when another vehicle was located, 1 / 2 of the students who did want to go on the field trip but had been left behind were able to join. what fraction of the class ended up going on the field trip ?
Options: a. 1 / 2, b. 2 / 3, c. 13 / 15, d. 23 / 30, e. 4 / 5
Output (English): c