The correct answer is C. 15000 units.
The reorder point is the level of inventory at which a new order should be placed. It is calculated by taking the number of units sold per time and multiplying it by the purchase order lead time. In this case, the number of units sold per time is 400 units and the purchase order lead time is 35 minutes. Therefore, the reorder point is 14000 units.
However, we need to round this number up to the nearest whole number, which is 15000 units. This is because we cannot order parts that are not whole numbers.
The other options are incorrect because they do not take into account the purchase order lead time. Option A is the number of units sold per time, option B is the purchase order lead time, and option D is the number of units sold per time plus the purchase order lead time.