They were heard ... goodbye to their friends.

They build sentences using the grammar they want instead of finding real sentences that match the grammar point they want to test.

Now, I understood why we easily conduct a conversation and it doesn't mean that we can easily pass an exam.

Maybe they just want to test our grammar, not our real English in our real life. That's the point. That's why language tests always challenge us.

Thank you for explaining, Mr.Micawber.

It's so much interesting discussing with you. That sounds like you are an expert in English. I do hope that I can learn more from you.

Take care! See you soon!