The correct answer is A. Kala asked Radha who she had been speaking to over the phone.
In this sentence, Kala is using the past participle “spoken” to form the present perfect continuous tense. This tense is used to talk about an action that started in the past and continues up to the present. In this case, Kala is asking Radha about a phone call that she had just finished.
The other options are incorrect because they use the simple present tense or the simple past tense. The simple present tense is used to talk about actions that happen regularly or repeatedly. The simple past tense is used to talk about actions that happened at a specific time in the past. In this case, Kala is not talking about a regular or repeated action, and she is not talking about an action that happened at a specific time in the past. She is talking about an action that started in the past and continues up to the present. Therefore, she must use the present perfect continuous tense.