Answer:
c) Instructions that are not understandable
Explanation:
Computer languages, as regular languages, have rules of syntax. But with the difference that the slightest misspelling in a computer program would make it impossible for the computer to understand it.
If, in English, I say: 'Please compte tuo plus two' you might understand that I'm says '2+2'
But to a computer, this spelling error might as wells writing gibberish