preposition group case

例句：

1. 1. The correct use of prepositions is essential for effective communication.
   正确使用介词对于有效沟通至关重要。
2. 2. In a prepositional phrase, the subject and predicate are separated by the preposition.
   在介词短语中，主语和谓语通过介词分隔开。
3. 3. The prepositional phrase "in the morning" indicates that the action takes place in the early hours of the day.
   介词短语“in the morning”表示该动作发生在一天的早晨。