The most appropriate option to fill in the blank is:

☀ had been ill

Explanation for all options:

☀ has been ill: This option is in the present perfect tense. It indicates an action that started in the past and continues into the present. However, in this context, the sentence requires past perfect tense to show the duration of an action that was ongoing before another past action.

☀ had been ill: This is the correct option. The past perfect tense "had been" is used to indicate an action (being ill) that started in the past and was still ongoing before another past action (his father coming) took place. This construction shows the sequence of events and the duration of the illness.

☀ is being ill: This option uses the present continuous tense, which is not suitable for this context. Present continuous describes actions happening at the moment or during a specific period around the present time, but the sentence refers to a past action and its duration.

☀ is ill: This option uses the present tense and describes a general state of being ill. However, it doesn't convey the duration of the illness and doesn't fit well in the context of the sentence, which talks about an action that was ongoing before his father came.