Fill in the blank with a suitable preposition.
The votes have increased _______ 10 percent.
The preposition ‘by is used to show the degree or amount by which something happens. In the given sentence the increase happens by a total of 10 percent, hence option B is correct. On the other hand, ‘on’ and ‘up’ are irrelevant here since they are prepositions of place that denotes a position or direction which is inappropriate here. Hence options C and D are incorrect. Whereas ‘off’ means to get rid of something which is once again irrelevant therefore option A is incorrect.