Ahypothesis is based on observation and must be written, testable, without any variables, shared with others

The answer has to be option B "testable." A hypothesis is a educated guess on what you think is going to happen during a experiment. Also its not going to be option A because a hypothesis doesn't exactly have to be written homeschool students have there instructions on a computer in order to be completed. Its not option C because a  hypothesis has the have its test variables. (independent & dependent variables) Its also not option D because some scientists conduct their experiments by themselves.

Hope this helps!