C.
[tex]11 + 22 + 33 + 44 + ... + 7700 = \\ 11 \times 1 + 11 \times 2 + 11 \times 3 + 11 \times 4 + ... + 11 \times 700 = \\ 11 \times (1 + 2 + 3 + 4 + ... + 700) = \\ 11 \times \frac{700 \times 701}{2} = \\ 11 \times 350 \times 701 = \\ = 2 \: 698 \: 850[/tex]