题目

Happy Middle School We're a bilingual(双语的) school for children of 6～15.We want a cook，a library assistant, a sports coach and a language teacher. JobsAgesLanguagesSkills(技能)Others cook25～40Chinesecan cook Chinese and Western foodhealthy library assistant20～35Chinese，  Englishcan read different kinds of bookscareful sports coach20～40Chinese, Englishmajor in(主修) P．E.healthy and strong language teacher—Chinese, Englishmajor in English— 1．Which of the following can go to Happy Middle School? A．A four­year­old child.    B．A ten­year­old c在数列{an}中，已知a1=1，an+1=an1+2an(n∈N+)．（1）求a2，a3，a4，并由此猜想数列{an}的通项公式an的表达式；（2）用适当的方法证明你的猜想．