non-current assets

Which of the following items (that all generate future economic benefits, and whose costs can be
measured reliably), is an intangible non-current asset?
1 Computer hardware owned by a business
2 Operating software that operates the computer hardware in (1)
3 A patent bought by a business
4 An extension to an office building owned by a business
A All four items
B 1, 2 and 4 only
C 1 and 2 only
D 3 only

hello Sir l consider the answer is 2 and 3 but has been taken only 3

why?
furhermore,l need your explanation about whether software is tangible or intangible non-current asset?