– How long have you been collecting stamps?– Ever I was twelve. I have been collecting s

– How long have you been collecting stamps?
– Ever I was twelve. I have been collecting stamps for about eight years.
A. since B. before C. by

解析：考察连词。since 自从……以来；before在……之前；by到……为止。句意：你收集邮票多久了？——自从我十二岁以来，我一直收集邮票，已经有八年了。since +一般过去时，表示从过去某时开始，故选A

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