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it may be because
疲れつかれているせいか眠いねむい。
Perhaps because I am tired, I am sleepy.
年ねんのせいか物忘れものわすれが増えふえました。
Perhaps due to age, I forget things more often.
緊張きんちょうのせいか手てが震えるふるえる。
Perhaps because of nervousness, my hands are shaking.