Given scientific fact as input, generate the question from this fact such that it can be answered from the input.

[Q]: Collision frequency is greater for homogeneous category of catalysts, which also tend to be more sensitive to temperature and more 'expensive'.
[A]: Collision frequency is greater for what category of catalysts, which also tend to be more sensitive to temperature and more 'expensive'?


[Q]: A pregnant woman should avoid toxic substances while pregnant.
[A]: What should a pregnant woman avoid while pregnant?


[Q]: Benzoic acid type of acid is often used as a preservative for acidic foods such as fruit juices.
[A]:
What type of acid is often used as a preservative for acidic foods such as fruit juices?