Which of the following suffices to convert an arbitrary CFG to an LL(1) grammar?
LL(1) parser is top down parser.
For top down parsers, the grammar should be unambiguous, deterministic and should not be left recursive.
All the $3$ conditions must be satisfied for LL(1) parsers.
Now, even if all $3$ conditions are satisfied we cannot get an LL(1) or even LL(k) (for any $k$) grammar for even a DCFG. This is because there are DCFLs which does not have an LL(k) grammar (see ref below). On the other hand for any DCFL, we can always have an LR(1) grammar.
So, option D is correct.
D. Removing left recursion and factoring the grammar do not suffice to convert an arbitrary CFG to LL(1) grammar.