What is in the middle? The letter "B" or the number "13"

Is this a spiral or concentric circles? (Cover half and see for yourself)

In the following five pictures, which figure is the largest ?
(Measure them and see if you are correct)

In these two figures, which line is longer (measure them and see if you are correct)

Of the two red dots which one is bigger?
(measure them to find out)

Are these lines parallel or curved?
(hold a straight edge next to them)

How many planks are there in this pile of lumber?
Three? Four? Or just two?

Are you going up this staircase or going down?