Which encoding replaces unusual ASCII characters with “%” followed by the character’s

Which encoding replaces unusual ASCII characters with “%” followed by the character’s two-digit ASCII code expressed in hexadecimal?

A. Unicode Encoding
B. UTF Encoding
C. Base64 Encoding

D. URL Encoding

Reference: https://ktflash.gitbooks.io/ceh_v9/content/125_countermeasures.html