下列哪种光线形成的投影不是中心投影（　　）

短文改错

    During the summer holidays, I thought I should do anything meaningful instead of touring. So I got a job at fast food restaurant and worked there for a cleaner. I worked 7 hours a day for three week. The job was hard and boring and seemed endless, it made me so tired that I nearly left it halfway. Therefore, I stuck to it with determination. Every day I start off for work early in the morning and got to home late in the evening. Finally, I finished the job before the new school term began. Now, I understand that labor means. I consider it a successful experience, which is worth remembered forever.

如图，平面四边形ABCD中，AB= $\sqrt{5}$ ，AD=2 $\sqrt{2}$ ，CD= $\sqrt{3}$ ，∠CBD=30°，∠BCD=120°．

下列说法错误的是（    ）

$\frac{2}{3}$  和 $\frac{5}{6}$  ____              $\frac{7}{8}$  和 $\frac{3}{4}$ ____

$\frac{3}{10}$  和 $\frac{1}{2}$  ____             $\frac{1}{5}$  和 $\frac{1}{3}$ ____