**Answer: A**

`every` is an `and` over a set of items:
`every(p, lst)` = p(lst_{1}) && p(lst_{2}) && ... && p(lst_{n})
= p(lst_{1}) ∧ p(lst_{2}) ∧ ... ∧ p(lst_{n}) .

The base case (identity or idempotent value) for `and` is `true`,
since (x && `true`) = x, so `every` should return
`true` as its base case when the list is empty.