How long have you been here?I _____ here only half a month a

題目：

How long have you been here?I _____ here only half a month ago.A came B have been
C have come
D had been

解答：

選A
half a month ago 有具體的時間,用一般過去式
而且come是短暫性動詞,所以選A 再問： 能順便解釋一下，每個選項的用法之類的嗎 謝謝
再答： have been 現在完成時，表示去過某地 have come 以前來過 had been 過去完成時，過去的過去，通常用在過去時句中，表示當時之前已經發生的動作