In each paragraph 3 multiple choice questions have to be answered. Each question has four choices (A), (B), (C) and (D) out of which ONLY ONE is correct.

Paragraph: If a continuous f defined on the real line R, assumes positive and negative values in R, then the equation f(x)=0 has a root in R. For example, if it is known that a continuous function f on R is positive at some point and its minimum values is negative then the equation f(x)=0 has a root in R. Consider f(x) = Ke^{x} - x for all real x where k is a real constant.

The positive value of k for which Ke^{x} - x = 0 has only one root is