The correct option is A Monocot
Grafting is the technique whereby tissues from one plant are inserted into those of another so that the two sets of vascular tissues may join together. Monocots do not have a vascular cambium, which is needed for the process of grafting as they do not undergo secondary growth. In grafting, the cambium helps in binding the two parts of the stem. Monocots do not possess cambium and hence grafting is not possible in monocots.
Thus, the correct answer is option (A), 'Monocot'.