Which of the following sampling problems accounted for the Literary Digest’s mistaken prediction that Landon would be elected President of the U.S. in 19936 instead of Roosevelt?

a. They used telephone directories and automobile registries as a sampling frame which created a social class bias.
b. There use of quota sampling from an inaccurate quota frame, led to an unrepresentative sample.
c. The population had changed so radically in such a short time that they had collected an unrepresentative sample.
d. There use of convenience sampling led to a biased sample.

Answer a,