1] True-False Determine whether the statement is true or false. a) If I = (0, 1), then {x : x E 0, 1]} is the set of all cluster points of I. b) The signum function sgn is continuous at 0. c) The finite set N has no cluster point. d) If the function f : A R has a limit L at the point c, then can define F: AU{c} R that is continuous at c.