(3) 朝からずっとコンピュータに向かっていたので,
目が疲れました。
答 I have been staring at the com-
puter screen since this morning, so
my eyes are tired [hurt].
B1 My eyes are tired [hurt] (,) because
I have been staring [looking] at the
computer screen since this morning.
2 I have been working on [working
at] a computer since this morning, which
has tired my eyes.
B3 I have tired eyes (,) because I have
been using the computer since this
morning.