(1) Knock on one end of a long iron pipe, and the sound will first pass through the iron pipe and then through the air, because the propagation speed of sound in the iron pipe is much faster than that in the air;

So the answer is: iron pipe.

(2) Red roses are red and can only reflect the same red as themselves; The blue glass plate is blue, the sunlight shines on the glass, the blue light can shine on the white paper through the glass, and the white paper can reflect the blue light into our eyes, so we see that the white paper is blue;

So the answer is: reflection; Blue.

(3) The focus of the incident light and the main optical axis is the focus of the convex lens, which is drawn behind the focus, and the light passing through the focus will be refracted by the convex lens into light parallel to the main optical axis and emitted;

Find the focus of the concave lens (on the light emitted by the convex lens), and draw the concave lens and the main optical axis of the concave lens accordingly, so that the light that hits the focus of the concave lens will become the light parallel to the main optical axis.

Therefore, the answer chart is as follows: