Scala quiz. What will be the result of combining Strings for a

What will be the result of combining Strings for a Monoid?

import cats.implicits._
import cats.kernel.Monoid

Monoid[String].combineAll(List("a", "b", "c"))

"abc"
"a"
"c"
List("a","b","c")
List("abc")

Explanation

Monoid.combineAll performs operation combine for all elements with zero element. In the current example, zero element for Strings is empty String "", which being concatenated with other elements of the lists results in "abc".

Source: Scala Exercises: cats monoid