Told can indeed be a participle or a verb, depending on the context.
Here it's verb: it's a past tense of "tell".
It could be a participle if the sentence were as follows:
I puffed by cheeks to get rid of the hiccups, told by my cousin to do so. (it's a weird formulation but not incorrect I believe)
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Tranquil- free from disturbance; calm.
I am going with B because using a phone call, the customer can notice emotion, if you send a text or something, the person won't know if you actually mean the apologies. Hope i helped. Have a nice day.
C seems to be the only one that makes sense.