A. too much energy
B. based on American designs
C. they are too costly
D. they are not reliable
E. quality control
F. free of charge
The use of robots increases ______.

A. actions
B. functions
C. reflections
D. behaviors

A. The structure of a star.
B. A collision between two stars.
C. The attraction of two large stars.
D. The shrinking of a large star by its own gravitational force.