关于西班牙语,这句话En la sala hay una mesa y dos sofas. 这句话中为什么要用la而不用el,为什么用una而不用uno,哪里体现出阴性了,还有为什么"一"就有uno和una两种不同性的,而"二"就只是dos?谁可以解答下?

I am who I am Hello~everyone!I am a chinese boy.And I want to learn Spanish.I can speak a little English.I like making friends . I hope to learn something on language in this website.