In the example of a joint promise, what did A, B, and C do?

In a joint promise, multiple parties agree to fulfill an obligation together. In this scenario, when A, B, and C borrowed Rs. 15000 from X jointly, it signifies that they have collectively taken on the responsibility of repaying the loan. This arrangement creates a mutual obligation, where each party is bound to fulfill the terms of the promise together.

When A, B, and C borrow the amount jointly, it implies that the lender, X, can seek repayment from any one of the borrowers or all of them collectively. This characteristic of a joint promise is crucial as it establishes shared liability, meaning that if one borrower cannot pay, the others remain responsible for the entire amount.

The other choices do not represent a joint promise in the same context. Borrowing individually from X or blowing the money from Y does not create the collective obligation that defines a joint promise. Therefore, the correct answer effectively captures the essence of a joint obligation amongst A, B, and C concerning their loan from X.