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Let ${\bf f}(t)$ be a vector-valued function.

Which of the following is not a vector-valued function?

${\bf f'}(t)$

$\int {\bf f}(t) \ dt$

${\bf f}(t) \times {\bf f''}(t)$

${\bf f}(t) \cdot {\bf f'}(t)$

$||{\bf f}(t) || {\bf f''}(t)$