It is well known that Tomas Edison ______ the electric lamp.
A) discovered C) developed
B) found D) invented

A．To give the students more free time to do their school work.
B．To give the students help in their homework out of classes.
C．To offer the students more chances to work in the future.
D．To allow the students to do school work anywhere.

A．very convenient to use in a lot of places
B．cheap enough for everyone to get one
C．small enough to put into one's pocket
D．easy to take to and from classrooms