The grass is all wet. It _______ during the night.  should have rained  must have been raining  ought to have been raining  had been raining

In the sentence "The grass is all wet. It _______ during the night," the phrase that best fits the context provided is "must have been raining."

Explanation:

1. Context Clue: The wet grass implies that there was some form of precipitation during the night.
2. Modal Verbs:
   • "must have been raining" indicates a high probability or certainty that it rained since the condition of the grass suggests it.
   • "should have rained" implies an expectation that it rained, which is less definite.
   • "ought to have been raining" suggests a moral obligation or expectation, which is not fitting in this context.
   • "had been raining" suggests a past continuous action but does not fit the grammatical structure needed here.

Thus, the most appropriate choice is “must have been raining.”

Final Answer:

The grass is all wet. It must have been raining during the night.