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B is corrent.  Losses are disallowed on sales between related taxpayers, including family members. Thus, Daniel’s loss of $3,000 is disallowed on the sale of stock to his son, William. William’s basis for the stock is his $7,000 cost. Since William’s stock basis is determined by his cost (not by reference to Daniel’s cost), there is no "tack-on" of Daniel’s holding period. Thus, a later sale of the stock for $6,000 on November 1 generates a $1,000 short-term capital loss for William. Note that if William had sold the stock at a gain, Daniel’s disallowed loss would have been used to reduce the recognized gain.
A is incorrect.  Since William has a cost basis for the stock, his holding period begins when he purchased the stock.
C is incorrect.  William does not receive any benefit for Daniel’s disallowed loss. 
D is incorrect.  William does not receive any benefit for Daniel’s disallowed loss.