非零向量 $\overrightarrow{a}$ 、 $\overrightarrow{b}$ 满足| $\overrightarrow{b}$ |=2，＜ $\overrightarrow{a}$ ， $\overrightarrow{b}$ ＞=30°，且对∀λ＞0，且| $\overrightarrow{a}$ ﹣λ $\overrightarrow{b}$ |≥| $\overrightarrow{a}$ ﹣ $\overrightarrow{b}$ |恒成立，则 $\overrightarrow{a}$ • $\overrightarrow{b}$ =（   ）

   Many teenagers feel that the most important people in their lives are their friends．They believe that their family members don’t know them as well as their friends do．In large families，it is quite often for brothers and sisters to fight with each other and then they can only go to their friends for some ideas．
   It is very important for teenagers to have one good friend or a group of friends．Even when they are not with their friends，they usually spend a lot of time talking among themselves on the phone．This communication is very important in children’s growing up，because friends can discuss something．These things are difficult to tell their family members．
   However，parents often try to choose their children’s friends for them．Some parents may even stop their children from meeting their good friends．Have you ever thought of the following questions?
    Who chooses your friends?
   Do you choose your friends or your friends choose you?
   Have you got a good friend your parents don’t like?
   Your answers are welcome．

Her mother often forgets       the door but this morning she remembered     it.