[Haskell-beginners] Type assignment for List

Hello Friends, I am totally new to Haskell. I am learning Haskell from a website on my own pace. From that site, I came to know about list in haskell and its type assignment. There is a confusable question on site. I am posting question here.... 1. Given that the expression []:xs is well typed, which of the following is not a possible type assignment for xs? Options:- 1. xs :: [Int] 2. xs :: [[Float]] 3. xs :: [[[Char]]] 4. xs :: [[[[Bool]]]] If any friend know about it then please clarify me on it. Thanks in advance Rajatkumar Zala India