"I eat lunch."
Translation:Eu mănânc prânzul.
the translation is actually wrong which is why you are confused. "eu mananc prinzul" means I eat the lunchtime. "Eu maninc de prinz" is i eat for lunch, you can also say "Eu iau pranzul", but it's given wrong here. "Eu mananc pranz" is "I eat lunchtime" which is not correct.