--how long have you been here in sydney? --

since
arrive
后面都可跟表示时间段的
时间状语
。题中
since
last
wednesday表示从上周三到现在这段时间；I
arrived
two
days
before
you
.我已经比你早到了两天了。
而go
是
瞬间动词
，跟表示时间点的时间状语，如I
went
at
8
o'clock.

arrive是到达的意思啊，根据句意就是我比你早到两天啊。go后面要接介词啊

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