| Explanation & Hints:
In the C programming language, identifiers (including variable names) must follow specific rules:
- Identifiers can consist of letters (both uppercase and lowercase), digits, and underscores.
- Identifiers must not begin with a digit.
- Identifiers must not be keywords of the C language.
- Identifiers should not contain spaces or special characters other than the underscore.
Based on these rules, the legal variable names from the options you’ve provided are:
- three_months_old – This is a legal identifier as it only contains letters and underscores.
- month3 – This is a legal identifier as it starts with a letter and is followed by a digit.
- _3monthsOld – While it is somewhat unconventional to start with an underscore followed by a digit, this is technically a legal identifier in C.
The identifiers that are not legal include:
- 3monthsOld – This is not legal because it starts with a digit.
- int – This is not legal because “int” is a reserved keyword in C.
- three months – This is not legal because it contains a space.
Thus, the three legal variable names are _3monthsOld, three_months_old, and month3. |