They must have a list of biomes there. When they say which one is endangered they mean which one is likely to no longer exsist after an amount of time.
Your answer is going to be Hydrolysis
I am pretty much sure that C. Lyases is the answer.
Let me give some information about this.
Lyases are the main groups which show peculiarity in having more than several categorised groups having more enzymes than the other four.
Hydrolase does not fit this bill instead they contain less categorised groups.
Other two groups are not even having that much groups.
Hope helps ...
