若实数a、b满足a＋b＝2，是$3^a+3^b$的最小值是（  ）

    I have many good friends at school. I think Gina is my  ____(good)friend. She is 1 years older ____me. We live in the same town and we are classmates now. Gina is taller and ____ outgoing than me. We are both interested in sports, but she always plays table tennis ____ (good), so she always wins. ____we have the same hobbies and interests, we also have some ____(difference).

    Gina always  exercises and she  ____(read)books every day.  ____, she never eats junk food and stays up late. ____, I like eating junk food and never helps ____housework.

多年前，一名研究人员在山林考察时偶然看到一株开红花的木继木，而一般木继木都是开白花的。