The issue with the sentence is the incorrect use of "their" instead of "they're." The correct sentence should be: "Omar and Mary are champion snowboarders. They're starring in an upcoming commercial for a national sporting goods store." "They're" is a contraction for "they are," while "their" is a possessive pronoun indicating ownership.
I was the champion in the school talent show with my best friends Kathrine and Madison.
He is this year's state high school wrestling champion.
Commercial farming is good.
He was the undisputed champion of the tournament. Many groups continue to champion human rights in developing countries.
You have a slim chance of beating the champion runner.
Nigel Richards was the first person ever to achieve the title of world scrabble champion more than once.
People made a commercial industry to make a profit.
The challenger had our champion pinned to floor in eight seconds flat!
go somewhere girl or boy
"Satyamev jayte" is the national sentence of India.
During wars there is a large feeling of national pride.
The national debt of this country is ridiculous.