I am not sure in compiler but lets go option by option.
1. Traveling the list till null,if null kis encountered then there is no Loop.So this seems to be true.But what will happen in case there is a loop.Then we will use option 2.
2.If same address is encountered again while traversing list, then we know there is a loop.
3.The multiple nodes can have same value,which means there can be no loop but still multiple nodes can have same valie ,so it cant be find the loop.
4.Both 1 and 2 are true,.
So i think d is the answer here as combination of 1 and 2 will help to find the loop.It is not possible with only 1 or ony 2 as if only 1 is true then it can't find loop if exists and if only 2 is true it dont know when to stop.I will say D is the answer