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a portion of the graph of f(x) = −x2 − 10x − 21 is shown. which of the following describes all solutions for f(x)?

a. (x, x2 − 10x − 21), where −7 ≤ x ≤ −3
b. (x, y), where −7 ≤ x ≤ −3
c. (x, x2 − 10x − 21), where −8 ≤ x ≤ −2
d. (x, y) for all real numbers