boon
1.Cheap editions are a great boon to students里的a great boon不可改作great boons。
2.下面三句意思相同，但第三句不很普通：
- This dictionary is a great boon to students of English.
- This dictionary is a great boon to the student of English.
- This dictionary is a great boon to the study of English.
拓展学习：小词详解 | boon
