在我国的主要植被类型中，植物种类特别丰富的是草原。

He was ____ (interest) in science when he was ten years old.

$\frac{\text{1}}{\text{5}}$ + $\frac{\text{1}}{\text{4}}$ =        75×20％=       $\frac{\text{4}}{\text{5}}$ × $\frac{\text{7}}{\text{16}}$ =        $\frac{\text{9}}{\text{20}}$ × $\frac{\text{5}}{\text{18}}$ =

3.14×3=        $\frac{\text{5}}{\text{8}}$ ÷ $\frac{\text{1}}{\text{4}}$ =        15.7÷5=      20÷ $\frac{\text{1}}{\text{4}}$ =

$\frac{\text{1}}{\text{8}}$ - $\frac{\text{1}}{\text{16}}$ =       49÷ $\frac{\text{7}}{\text{14}}$ =       81× $\frac{\text{2}}{\text{9}}$ =       56× $\frac{\text{5}}{\text{7}}$ =

1- $\frac{\text{2}}{\text{5}}$ =          $\frac{\text{3}}{\text{4}}$ + $\frac{\text{4}}{\text{5}}$ =        84×50%=       $\frac{\text{2}}{\text{5}}$ ×40=