What are the four main issues that Krashen's input hypothesis involves?

What are the four main issues that Krashen's input hypothesis involves?

(P151 )They are as follows: (1) It relates to acquisition; (2)People acquire language best by understanding input;(3)The ability to speak emerges; and (4)Enough comprehensible input provides i+1 automatically.
【评分标准】全题共5分,答案含四点,全对得5分,每错一个扣1分,不答不得分。如答案要点不完整,酌情扣分。如表述有语法、拼写、标点等问题,也酌情扣分,但全题在这方面的扣分不得超过1分。