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