Select the sentence with the appropriate use of preposition.

It has been raining since morning.

The sentence with the appropriate use of preposition is It has been raining since morning.

The preposition "since" is used to indicate that something began at a specific time in the past and continues to the present. In this case, the speaker is saying that it has been raining since the morning, which means that it has been raining for some time now and is still raining.

The other prepositions in the options are not appropriate for this sentence. The preposition "till" is used to indicate a specific time in the past when something ended. The preposition "from" is used to indicate a starting point, but it does not necessarily imply that something is still happening. The preposition "by" is used to indicate a specific time in the future when something will be finished.