Final answer:
The most effective strategy for building and extending students' vocabulary knowledge is showing students how to use roots and affixes to determine meanings.
Step-by-step explanation:
The most effective strategy for building and extending students' vocabulary knowledge is option A: Showing students how to use roots and affixes to determine meanings.
Understanding the meaning of roots and affixes can help students decipher unfamiliar words and expand their vocabulary. By breaking down words into their constituent parts, students can recognize common patterns and meanings, making it easier for them to learn new words.
For example, if students understand that the root 'bio' means 'life' and the suffix '-logy' means 'study of,' they can easily understand that 'biology' means 'the study of life.'