Meals arevery boring. He ________ has the same thing to eat every day.()
A:never
B: usually
C:sometimes
男低音歌唱时女高音轻声伴唱,男低音与女高音相比较,男低音的响度____ (填“大”或“小”),女高音的音调____ (填“高”或“低”)。
胃属于哪个系统( )