The system of proportional representation

a. tends to produce more legislative parties, but it has never been tried in the United States on any significant scale.
b. has declined in popularity around the world because having too many legislative parties creates too much uncertainty in government.
c. guarantees that no party will receive a majority.
d. encourages voters to behave strategically by turning to one of the less objectionable major party candidates who has a chance to win.

a. tends to produce more legislative parties, but it has never been tried in the United States on any significant scale.