Consider below statements – (I) Each non-leaf node in B⁺ tree has between…

Consider below statements – (I) Each non-leaf node in B⁺ tree has between ⌈n/2⌉ and n children, where n is fixed for a particular tree. (II) The search key of a clustering index is always primary key. (III) Secondary indices must be dense. (IV) In a dense index, an index entry appears for only some of the search-key values. Which of the above statements are true?