This is from Brutal SC document -
The ancient Romans piped hot water through the walls and under the floors so as to warm up the rooms.
A. so as to warm up the rooms
B. and so would be able to warm up the rooms
C. to warm the rooms up
D. so that they could warm up the rooms
E. in order that they would warm up the rooms
OA is given as D.
Instructors, I am giving my exam in a week. Can you please explain when to use so that/so as to/ to. I am always confused.
I picked A because I have seen GMAC use 'so as to' in other questions.
Also, which is correct - warm up the rooms or warm the rooms up?