从下面方框中选择正确的单词并用其适当形式填空，使短文意思完整、通顺。

Dear Jenny,

    My name is Alan. I'm a 12-year- old girl. I'm the only ____ in my family. My birthday is on ____ 1st. It's the ____ day of the sixth month. It's also the Children's Day(儿童节). My parents ____ a party for me on that day. My friends ____ to the party. They bring(带来) me many birthday presents(礼物), and they sing Happy Birthday to me. ____ eat some strawberries, oranges and ____. We eat chicken and cakes ____ dinner. We also play games. We have a ____ time! How old are you? ____ is your birthday? Can you tell me?

                                                                                                                                                                                      Alan

① $\frac{a}{a+b}$ ＜ $\frac{c}{c+d}$ ；② $\frac{c}{c+d}$ ＜ $\frac{a}{a+b}$ ；③ $\frac{d}{c+d}<\frac{b}{a+b}$ ；④ $\frac{b}{a+b}$ ＜ $\frac{d}{c+d}$

其中不等式正确的是（）