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1 . How many bitstrings of length 77 start with 1111 or end with 0000?

(a)

$2^{74} - 2^{69}$

(b)

$2^{77} - 2^{69}$

(c)

$2^{77} - 2^{73} - 2^{73}$

(d)

$2^{73} + 2^{73}$