Paper tube photography

We should observe the inside of the tube facing the A end instead of the B end, so that the light can be seen clearly from the paper tube B through the convex lens.

In actual photography, when shooting a distant object, the lens is retracted, so in order to make the image of the distant object clear on the transparent paper, the transparent paper should obviously be closer to the lens, which is equivalent to narrowing the distance between the lens and the negative, so option D is wrong.

So choose C.