Which of the following DOES NOT help to explain why it is so expensive to grow grapes in the vineyards? Select one: a. Producing grapes in the Douro requires constant work, mostly done by hand b. The Douro has the largest area of mountain vineyards on Earth c. The high cost of labor by the farmers to grow grapes translates into the price they must sell them for d. Not all of the grapes grown in a vineyard are fit to be made into port e. Some vineyards in the Douro have more than thirty different grape varietals f. None of the above