While searching in a binary search tree, if a value smaller than the key is found, then all the following keys will be larger than this smaller value. Similarly, if a value larger than the key is found, all the following keys will be smaller than this larger value. Here, options $A,B$ and $C$ are valid key sequences but option D is not as here, we first encounter $66$ which is larger than the search key $44,$ and after this $77 > 66$ is given which is not possible in a binary search.
