(a) That's wrong. Although the variation in quality could have been discovered by inspecting the wheat at the time of delivery, the law does not make it a term of contracts of sale that the buyer must inspect goods when they are delivered. The relevant sale of goods legislation only gives buyers a right to inspect goods when they are delivered. So it is up to the buyer to decide whether or not they wish to inspect the goods at the time of delivery.  See a list of the relevant sections.

However, the relevant legislation also makes it clear that if a buyer chooses not to inspect the goods, and the goods suffer from some fault or defect that could have been discovered by examining them, the buyer will be taken to have accepted the goods and will lose any right to subsequently reject them because of the faults. This means that a buyer who chooses not to inspect goods delivered takes on the risk of the goods having a fault or defect that they could have discovered. This is what has happened in the example: B's decision not to inspect the wheat means that it is now too late for B to reject it.