Identify the Legally Insufficient Consideration

Identify the legally insufficient consideration.

A) Alex promised to pay Tom for his car in four installments of $1,000 each. He fails to pay these installments. Tom threatens suit, to which Alex promises to pay just $100 in exchange for Tom's promise to release him from the remainder of the amount.
B) Alex promised to pay Tom for his car in four installments of $1,000 each. He fails to pay these installments. Tom threatens to sue him, to which Alex promises to pay an interest of 2 percent whenever he gets his debtors to repay him.
C) Alex promised to pay $1,000 to Tom for his car, due March 1. On March 1, Tom pays only $400 in exchange for Tom's promise to release him from the remainder of the amount.
D) Alex promised to pay $1,000 to Tom for his car, due March 1. On February 27, Tom pays only $400 in exchange for Tom's promise to release him from the remainder of the amount.
E) Alex promised to pay $1,000 to Tom for his car, due March 1. On March 18, Tom pays only $400 and takes Alex to the carnival.