Final answer:
Encouraging students to compare the parts of new multisyllable words with known single-syllable words is the most effective strategy in promoting second graders' decoding of multisyllable words.
Step-by-step explanation:
The most effective strategy in promoting second graders' decoding of multisyllable words would be option C, encouraging students to compare the parts of new multisyllable words with known single-syllable words.
By comparing multisyllable words to known single-syllable words, students can identify familiar patterns and phonemes, which can help them decode unfamiliar words more easily.
For example, if a student knows that the single-syllable word 'cat' has the /æ/ sound, they can apply this knowledge to decode the multisyllable word 'catalog', recognizing that the 'cat' syllable will have the same /æ/ sound.