Brenda observes that the keyboard and the screen of an open laptop lie on two different planes. in how many lines do the planes containing the keyboard and the screen intersect?

I'm sure a majority, if not everybody, has seen a laptop. You will observe that a laptop has two planes represented by the keyboard and the laptop screen. In geometry, the plane is one of the three undefined terms. The other undefined terms are the point and the line. They are called as such because they are so basic that you don't really define them. They are used instead to define other terms in geometry. However, you can still describe them.  A plane is described as any flat surface with an area in one dimension only. As shown in the diagram in the attached picture, you can see the two planes in two views: front view and side view. The two planes intersect and coincide at one line, represented by the one in red. They intersect at only one line.

The answer is a because i went through all the other ones that it didn’t come out right