Explanation:

The correct tense for the sentence "It (rain) since morning" is option 'D' - "has been raining".

Present perfect continuous tense:

The present perfect continuous tense is used to describe an action that started in the past and is still ongoing in the present. It is formed by using "has/have been" + the present participle ("-ing" form of the verb).

Meaning:

In this sentence, the speaker is referring to the continuous action of rain that started in the morning and is still ongoing at the present moment.

Analysis of options:

Let's analyze the other options to understand why they are not the correct tense for the given sentence:

- Option 'A' - "rained": This is the simple past tense, indicating an action that occurred and ended in the past. However, the sentence requires a tense that shows the ongoing action of rain.

- Option 'B' - "rains": This is the simple present tense, indicating a general truth or habitual action. However, the sentence is referring to a specific ongoing action that started in the morning.

- Option 'C' - "is raining": This is the present continuous tense, indicating an action that is happening at the present moment. However, the sentence requires a tense that shows the action started in the past and is still ongoing.

Conclusion:

Based on the analysis, the correct tense for the sentence "It (rain) since morning" is option 'D' - "has been raining", which represents the present perfect continuous tense and accurately conveys the ongoing action of rain that started in the morning.