If you are to determine the focal length of a convex lens, you should have
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A convex lens and a screen
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A convex lens and a lens holder
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A lens holder, a screen holder and a scale
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A convex lens, a screen holder and a scale
D.
A convex lens, a screen holder and a scale
A convex lens, a screen holder for them and a scale are required in order to determine the focal length of a convex lens.