4: <BEC and <ECB are supplementary.
False, <BEC and <ECB are angles of triangle BCE and sum of two angles of a triangle can't be equal to 180 ( two angles of a triangle can't be supplementary).
5: C is the midpoint of BD.
False: It's not given C is the mid-point. So, we can't assume C is a mid point.
6: <BCE and < ECD are a linear pair.
True, because <BCE and < ECD are two angles on a common point on a line.
7: <ABE and <EBC are complementary.
True, because <ABC is a right angle and <ABE + <EBC = <ABC.