Final answer:
The word 'optional' has a different stressed syllable (the first syllable) compared to 'impression' and 'official', which both have the stress on the second syllable.
Step-by-step explanation:
When looking at the words impression, official, and optional, we need to focus on the syllable that contains the main stress. In English, the stress pattern of a word can significantly affect its pronunciation and can sometimes change its meaning.
Main Stress in Each Word
impression - The stress is on the second syllable: im-PRESS-ion.
official - The stress is on the second syllable: o-FISH-al.
optional - The stress is on the first syllable: OP-tional.
As we can see, the main stressed syllable in impression and official is the second one, while in optional, it is the first. Therefore, optional has the main stressed syllable that is different from that of impression and official. This aspect is crucial for proper pronunciation and can be confirmed by consulting a dictionary if there is any confusion.
It is important to note that the vowel that carries the strong stress in these words does not always come immediately before the [k] sound. However, in the examples provided in the question, none of the words has a [k] sound directly following the stressed vowel.
Final Answer
The answer to the multiple-choice question (MCQ) is:
c. optional