The correct answer is B. (consp)
(consp) is a function in Lisp that returns t if its argument is a cons cell and nil otherwise. A cons cell is a special type of data structure in Lisp that consists of two parts: a car and a cdr. The car is the first element of the cons cell, and the cdr is the rest of the cons cell.
The following are examples of cons cells:
(cons 1 2)
(cons ‘a ‘b)
(cons ‘(1 2 3) ‘(4 5 6))
The following are examples of objects that are not cons cells:
1
‘a
(1 2 3)
(4 5 6)
To test whether an object is a cons cell, you can use the (consp) function. For example, the following code will return t because the object (cons 1 2) is a cons cell:
(consp (cons 1 2))
The following code will return nil because the object 1 is not a cons cell:
(consp 1)