I remember this from when I was in highschool (or the dutch equivolant). The teacher of my english class proposed this riddle and a lot of people had it wrong but the answer was really simple. Remember in holland english isn't our native language.
What is the correct sentence?
"The egg yolk is white"
"The egg yolk are white"
Have fun and don't spoil
Look at the mistakes in the text, they are there for a reason :)