C) By altering the length of the pendulum
Explanation:
The period of a simple pendulum is given by the equation
[tex]T=2\pi \sqrt{\frac{L}{g}}[/tex]
where
L is the length of the pendulum
g is the acceleration due to gravity
In this problem, we are asked which adjustmenet can be done to speed up or slow down the pendulum clock: that means, which adjustment can be done in order to change the period of the pendulum.
From the equation above, we notice that the period of a pendulum depends only on its length (and the acceleration of gravity). Therefore, its period can be changed only by changing the length of the pendulum. And so, the only correct answer is
C) By altering the length of the pendulum
Learn more about period:
brainly.com/question/5438962
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