TV highlights:

All times Eastern."A" crashes the opening of Aria's art exhibition on "Pretty Little Liars" (ABC Family at 8). "The Bomb" (PBS at 8) chronicles the history of nuclear weapons, featuring newly declassified footage of detonations and commentary from former defense secretary William Perry and former secretary of state George Shultz as well as historians Martin Sherwin, Richard Rhodes, Sergei Khrushchev and Robert Norris.