Albert Einstein first hypothesized that a large object, such as a planet, bends the space around it. This hypothesis became part of the theory of relativity, which is about how objects affect the space and time around them.

What did this hypothesis most likely need before it became part of an accepted theory?
a. other scientists asking the same question
b. other questions about mass and space
c. experimental evidence that mass is not related to space
d. experimental evidence supporting the hypothesis