One day while shopping in a small town in southern California, it was my misfortune to be approached by a clerk．He seemed most unfriendly and not at all concerned about my intended purchase．I bought nothing, and marched angrily out of the store．
On the outside was a dark-skinned young man in his early twenties．His expressive brown eyes met and held mine, and in the next instant a beautiful, bright smile covered his face．I gave in immediately．The power of that broad smile dissolved all bitterness within me, and I felt the muscles in my own face happily responding．
"Beautiful day, isn't it?" I remarked, passing．Then I turned back．"I really owe you a debt of thanks," I said softly．
His smile deepened, but he made no attempt to answer．A Mexican woman and two men were standing nearby．The woman stepped forward and volunteered, "Sir, but he doesn't speak English．Do you want me to tell him something?" In that moment I felt transformed．The young man's smile had made a big person of me．My friendliness and good will toward all mankind stand ten feet tall．
“Yes,” my reply was enthusiastic and sincere, “tell him I said, ‘Thank you!’”
“Thank you?” The woman seemed slightly puzzled．
I gave her arm a friendly pat as I turned to leave．"Just tell him that," I insisted．"He'll understand．I am sure!"
Oh, what a smile can do! Although I have never seen that young man again, I shall never forget the lesson he taught me that morning．From that day on, I became smile-conscious, and I practice the art diligently anywhere and everywhere, with everybody．
Why did the author leave the store angrily?

A．He couldn't buy what he wanted．

B．The clerk treated him unkindly．

C．The clerk didn't speak English．

D．The store's goods were too dear．

By saying "I felt the muscles in my own face happily responding"(in Para. 2), the author means _       __________.

A．he smiled back at the young man

B．he did not want to smile

C．he would thank the young man

D．he was still in a bad mood

The author asked the woman to say "Thank you!" to the young man because the young man        .

A．had helped the author before

B．taught the author how to smile

C．taught the author a valuable lesson

D．was a kind employee of the store

In the passage, the author seems to suggest that we should __  ___.

A．be generous to strangers

B．practice smiling every day

C．help people in trouble

D．smile at other people