Write the most stable Lewis structure for each of the following compounds:

(a) Tetrafluoroethylene, C2F4. (The starting material for the preparation of Teflon)
(b) Acrylonitrile, C3H3N. The atoms are connected in the order CCCN, and all hydrogens are bonded to carbon. (The starting material for the preparation of acrylic fibers such as Orlon and Acrilan).