half an hour later she woke up.还有这half an hour为什么等于thirty mi

half an hour later she woke up.还有这half an hour为什么等于thirty mi half an hour later 为什么half an hour later 中an不变成a a half hour later\after half an hour\after half an hour late thirty minutes_____ (be)half an hour Thirty m____ is half an hour half an hour? 是half hour还是half an hour? half an hour or a half hour? a half hour还是half an hour? half hour =half an hour she -------(be)back in half an hour