① 只能是attaining,而不能是attain.这里的attaining是动词ing的形式,现在分词,简化从句.完整的句子应该是这样的,
(Because) cheetahs attains speeds of up to 60 miles per hour,cheetahs are perhaps the fastest of land animals.
用动名词(及v+ing的形式),省略了从句连接词和主语.
而attain是一般动词,如果用,前面必须有主语的.
② attaining是attain+ing,动名词,现在分词; attained则是过去式,过去分词; 而attain则是原型.