“How I Met Your Mother” (8 p.m., CBS): She can sell records by the millions, but can

“How I Met Your Mother” (8 p.m., CBS): She can sell records by the millions, but can Carrie Underwood act? The country music superstar drops by “How I Met Your Mother” to play Ted’s latest girlfriend. Our advice? He’d better think before he cheats.

“The Bachelor” (8 p.m., ABC): It’s decision time on “The Bachelor,” where maybe a rose and ring will be handed out and two reality-show stars will begin a life of eternal bliss. Yeah, and maybe they’ll ride off into the clouds on a unicorn.

“The Big Bang Theory” (9:31 p.m., CBS): Sounds like “The Big Bang Theory” might feature a big temper tantrum. Tonight, Sheldon gets a traffic ticket because of Penny, causing him to miss his chance to meet comic book legend Stan Lee.