Ancient Romans

[komal]

45. 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

[fibbonnaci]

A. so as to warm up the rooms [ so X as to be Y is the correct form of the idiom]

B. and so would be able to warm up the rooms [ wrong usage of 'and'. 'AND' needs to connect two independent clauses. the second is not a clause at all]

C. to warm the rooms up [ warm up is the correct idiom]

D. so that they could warm up the rooms [ correct! note 'so that' functions as 'in order' or rather as giving a reason. 'so that is not always wrong in GMAT.
There are two ways of constructing "so that" sentences.

Type 1 : I stopped running so that you could catch up. (here "so that" is used as "in order to")
Type 2 : The line was so long that i could not find the end of it.

E. in order that they would warm up the rooms [ nothing wrong in the sentence but wordier than D]