Which polynomial is in standard form?

A) 2x + 3x3 + 5x5 + 9x4 + 2x
B) 5 + 3x + x2 + 2x4 + 2x5
C) 8x7 + 3x6 + x5 + 5x4 − 2x3
D) 8x2 + 3x5 + x6 + 5x7 − 2