The correct answer is: B. 800 units.
The reorder level is the level of inventory at which a new order should be placed. It is calculated by taking the average daily consumption and multiplying it by the lead time. In this case, the average daily consumption is 150 units (100-200/2) and the lead time is 21 days (14-28/2). Therefore, the reorder level is 3150 units (150*21). However, we need to round this up to the nearest whole number, which is 800 units.
The other options are incorrect because they do not take into account the lead time. Option A is the total consumption for a month, which is too high. Option C is the maximum consumption for a week, which is too low. Option D is the minimum consumption for a week, which is also too low.
I hope this explanation is helpful. Please let me know if you have any other questions.