Answer:
PHP
Step-by-step explanation:
The best way to answer this question is to interpret it as, which of the three is a scripting language.
Analyzing each of the languages
1. C#
C# is not a scripting language, but instead it is an object-oriented programming language. Also, c# is a compiled language and one of the features of scripting language is that, they are interpreted.
2. PHP
Basically, PHP are used for server side scripting language because it uses scripts and its programs are not for general purpose runtime environment (but instead for special runtime environments).
3. HTML
HTML is neither a programming language, nor a scripting language because its design pattern does not follow that or programming and scripting languages, and it can not perform what an actual programming and scripting language do.