Please advice which suitable answer is suitable for the following sentences:
1)Mike learnt how to ski when he was five years old. (It is clear that Mike is older than five years now. So we use past tense).
b)has been learning
2)The bone was buried in the garden a few days ago. ('ago' is a representation of distance in past. So the sentence should be a past tense in passive form).
b)had been buried
d)has been buried.
Kindly explain the answer you have chosen. Really appreciate your assistance. Thanks.