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1 . How many bitstrings of length 55 start with 101 or end with 1111?

(a)

$2^{55} - 2^{48}$

(b)

$2^{52} + 2^{51}$

(c)

$2^{52} + 2^{51} - 2^{48}$

(d)

$2^{55} - 2^{52} - 2^{51}$