It . . . . . . . since early morning.

The correct answer is D. has been raining.

The other options are incorrect because they do not accurately describe the current weather conditions. Option A, “will rain,” is incorrect because it is not raining at the moment. Option B, “is raining,” is incorrect because it is not raining continuously. Option C, “rained,” is incorrect because it is not raining at the moment and it has not been raining continuously.

The sentence “It has been raining since early morning” describes a continuous action that began in the past and continues into the present. This is consistent with the current weather conditions, which are cloudy and wet.