Which of the following is true?
a. According to inflation theory, parallel lines appear to remain parallel because the universe is so unbelievably large.
b. According to inflation theory, parallel lines appear to remain parallel because mass has the effect of balancing the natural curvature of space-time.
c. According to inflation theory, parallel lines appear to remain parallel because space is inherently flat.
d. According to inflation theory, parallel lines appear to remain parallel because the universe is so very old.