Choose the valid identifier

A valid identifier can have letters (both uppercase and lowercase letters), digits and underscores. The first letter of an identifier should be either a letter or an underscore. You cannot use keywords like int , while etc. as identifiers.

An identifier is nothing but a name assigned to an element in a program. Example, name of a variable, function, etc. Identifiers are the user-defined names consisting of 'C' standard character set. As the name says, identifiers are used to identify a particular element in a program.

Explanation:

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answer(d) sequencing and iteration;