Which of these is not an element of a Hard Ball?

Which of these is not an element of a Hard Ball?

Which of these is not an element of a Hard Ball?

• Stone
• Cork
• Leather
• String

TELENOR 

ANSWER 

   (1)

• Stone

source https://sportsnewsstar.blogspot.com/2021/11/which-of-these-is-not-element-of-hard.html