The very first line of a shell script should always contain what two characters at the beginning of the line?
Answer: #!
Explanation:
From http://en.wikipedia.org/wiki/Shebang_%28Unix%29:
In computing, a shebang (also called a hashbang, …) refers to the characters "#!" when they are the first two characters in an interpreter directive as the first line of a text file. In a Unix-like operating system, the program loader takes the presence of these two characters as an indication that the file is a script, and tries to execute that script using the interpreter specified by the rest of the first line in the file.