The following sentence has been split into four segments. Identify the segment that contains a grammatical error.

They will go to bed / early since they / have to get up / at five on the morning. 

The erroneous part of the sentence is: at five on the morning

Key Points

• The error here lies in the use of the preposition.
• Replace "on" with "in" to make the sentence correct.
• “In” and “on” are both time-based prepositions. We can use them in different ways when we want to talk about specific periods.
• We use in with morning, afternoon, evening and night when we are referring to a general time.
  • For example- I always work best in the morning.
• But we use on when we talk about a specific morning, afternoon, etc., or when we describe the part of the day.
  • For example- On the morning of the 19th, I will have to rush to school.
• The given sentence is talking about a general time in the morning, so the preposition "in" should be used here.
• Therefore, the correct answer is option 2, which contains the error in it.

Corrected sentence: They will go to bed early since they have to get up at five in the morning.