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#### Question

A student has obtained an image of a distant object on a screen to determine the focal length F_{1} of the given lens. His teacher, after checking the image, gave him another lens of focal length F_{2} and asked him to focus the same object on the same screen. The student found that to obtain a sharp image, he has to move the lens away from the screen. From this finding, we may conclude that both the lenses given to the student were :

(A) Concave and F_{1} < F_{2}

(B) Convex and F_{1} < F_{2}

(C) Convex and F_{1} > F_{2}

(D) Concave and F_{1} > F_{2}

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