Final answer:
The word 'tonic' should be divided using the c) Open Syllable Principle because the first syllable 'to' ends with the vowel 'o' which is pronounced with a long sound.
Step-by-step explanation:
To divide the word "tonic," we would use the c) Open Syllable Principle. An open syllable occurs when a syllable ends with a vowel and that vowel is usually long. In the word 'tonic,' the first syllable 'to' ends with the vowel 'o,' making it an open syllable and giving the vowel a long sound. Therefore, 'to' is an open syllable, and 'nic' is a closed syllable because it is followed by a consonant. Hence, when dividing the word 'tonic' into syllables, you apply the Open Syllable Principle to the first syllable.