Sol:  c. The seller retains control over the goods.

According to IAS 18, revenue is recognised when following conditions have been satisfied (in case of

sale of goods):

a. The seller has transferred the significant risks and rewards of ownership of the goods to the buyer.

b. The seller does not retain control over the goods or managerial involvement with them to the degree usually associated with ownership.  

c. The amount of revenue can be measured reliably.

d. It is probable that the economic benefits associated with the transaction will flow to the seller.

     e. The costs incurred or to be incurred by the seller in respect of the transaction can be measured reliably.

      In short, if the seller retains control over the goods revenue can't be recognised as per Indian

Accounting standard 18.