a) a black material.
Graphite is described as a black material in the passage.

a) inside the pencil.
Pencil lead is put inside the pencil.

b) protects the lead.
The wooden part of the pencil is the part we hold and protects the lead inside.

b) 500 years ago.
Graphite was first used for writing in the 1700s, which is around 500 years ago.

a) a nib.
A pencil doesn't have a nib, unlike pens.

c) in factories.
Modern pencils are made in factories.

b) made every year.
More than 14 billion pencils are made every year.