Please answer a question about the following article about Ann Arbor, Michigan:

WPXD channel 31, an affiliate of the ION Television network, is licensed to the city. WHTV channel 18, a MyNetworkTV-affiliated station for the Lansing market, broadcasts from a transmitter in Lyndon Township, west of Ann Arbor. Community Television Network (CTN) is a city-provided cable television channel with production facilities open to city residents and nonprofit organizations. Detroit and Toledo-area radio and television stations also serve Ann Arbor, and stations from Lansing and Windsor, Ontario, can be heard in parts of the area.

WPXD channel 31 is an affliate of which TV network?
ION