What is the MD5 algorithm used for？（）
- Atakes a fixed-length message and produces a 128-bit message digest
- Btakes a variable-length message and produces a 168-bit message digest
- Ctakes a message less than 2^64 bits as input and produces a 160-bit message digest
- Dtakes a variable-length message and produces a 128-bit message digest ActualTests.com