I was an introvert   by nature. For as long as I remember, showing a sincere smile when meeting someone had never been easy. When meeting people, instead of being excited, I often felt upset or self-disturbed.  But we all know having friends is important. The more friends you have, the more opportunities you get, no matter whether it's a job opportunity, a romantic relationship, or a business partner. So a smile is important to making others feel comfortable. Mother Teresa said, "Every time you smile at someone, it is an action of love, a gift to that person and a beautiful thing."  The smile I'm talking about is not to make a face to someone. I'm talking about those wide smiles you make when meeting old friends. So I've discovered a trick. I call this technique "Oh, it's Jamie!" When I meet someone, I imagine him as an old friend of mine called Jamie. He was my first friend when we were still kids. It's no secret why my smile is as wide as I can possibly make.  And the best part, whenever you're friendly to others, they are friendly in return. You're not hearing this from me. A research which was done early by scientists actually backs   this claim. So do remember to give it a try. According to the author, showing a sincere smile is   _  .
an easy thing to make a face to be humorous very difficult
Question: I was an introvert   by nature. For as long as I remember, showing a sincere smile when meeting someone had never been easy. When meeting people, instead of being excited, I often felt upset or self-disturbed.  But we all know having friends is important. The more friends you have, the more opportunities you get, no matter whether it's a job opportunity, a romantic relationship, or a business partner. So a smile is important to making others feel comfortable. Mother Teresa said, "Every time you smile at someone, it is an action of love, a gift to that person and a beautiful thing."  The smile I'm talking about is not to make a face to someone. I'm talking about those wide smiles you make when meeting old friends. So I've discovered a trick. I call this technique "Oh, it's Jamie!" When I meet someone, I imagine him as an old friend of mine called Jamie. He was my first friend when we were still kids. It's no secret why my smile is as wide as I can possibly make.  And the best part, whenever you're friendly to others, they are friendly in return. You're not hearing this from me. A research which was done early by scientists actually backs   this claim. So do remember to give it a try. According to the author, showing a sincere smile is   _  .
A. an easy thing
B. to make a face
C. to be humorous
D. very difficult
Answer: