For a Presidential Candidate, Why Is It Especially Important to Win

For a presidential candidate, why is it especially important to win the Iowa caucuses and the New Hampshire primary?

A) Winning these states can benefit your campaign without costing too much money.
B) The convention winner is determined by who wins the most states, so a small state victory is just as beneficial as winning California or Texas.
C) It is important to win in these heavily conservative states because potential contributors donate more to conservative candidates.
D) These two states enjoy a disproportionate share of wealthy voters who are able to bankroll your campaign if you win.
E) Winning in these early states builds momentum.