The correct answer is: C. When they agree upon the same thing in the same sense.
Consent is an essential element of a valid contract. It is defined as the meeting of the minds of the parties to the contract. In other words, the parties must agree on the same thing in the same sense.
Option A is incorrect because it is not necessary for the acceptance to be made by the party to whom the proposal is made. The acceptance can be made by any person authorized to do so.
Option B is incorrect because it is not necessary for the acceptance to be made by another person other than the person to whom the proposal is made.
The acceptance can be made by the party to whom the proposal is made.Option D is incorrect because it is not necessary for the parties to agree upon a thing in the way it is understood by them. The parties must agree upon the same thing in the same sense.
For example, if A offers to sell B a car for Rs. 100,000, and B accepts the offer, there is a contract. However, if B thinks that A is offering to sell a bicycle for Rs. 100,000, there is no contract because the parties have not agreed upon the same thing in the same sense.