When disposable income is 4,000,C is

A) 2,000.
B) 3,000.
C) 3,400.
D) 4,000.

Given the information, it's not possible to accurately determine the answer without knowing the specific consumption function or the context in which "C" (presumably consumption) is defined. However, if we assume a basic consumption function where consumption increases with disposable income but does not equal the entire disposable income, option B (3,000) could be a plausible choice, suggesting that not all disposable income is consumed. This is a common scenario in economics where individuals save a portion of their disposable income.