Why Don't Texans Vote for Third Parties

Why don't Texans vote for third parties?

A) Because Texas employs what is known as a "first past the post," single-member district electoral system, it makes it difficult for third party candidates to win elections.
B) Third-party candidates really do not make a real effort to win.
C) Third-party candidates do not establish clear-cut positions on issues where there is broad agreement.
D) Third-party candidates develop a campaign strategy that is too narrowly focused.