Final answer:
The plural of compounds ending in 'ful' is formed by adding an 's' at the end, resulting in 'spoonfuls,' 'mouthfuls,' 'cupfuls,' and 'platefuls.'
Step-by-step explanation:
The plural of compounds ending in ful is formed by adding an 's' after the full word, without changing the base word. Therefore, the correct plural forms for the given words are:
- A. Spoonfuls
- B. Mouthfuls
- C. Cupfuls
- D. Platefuls
This is a standard rule for creating plurals for nouns that end with the suffix 'ful', which is a common compound structure in English.