He couldn’t remember ______. A: what was the formulae B: what the formulae was C: what were the formulae D: what the formulae were

Sanjay is constructing a simple spreadsheet to calculate the average monthly cost of production for a particular product. The company has produced a total of 100 units of the product over a three-month period. Sanjay’s spreadsheet is shown below.Which of the following formulae could Sanjay enter in cell B9 to correctly calculate the average monthly cost of production? A: 1 only B: 1 and 3 C: 1 and 4 D: 1, 2, 3 and 4