—Oh, sorry. But what did you say just now? I _______ something else.
A:thought
B:was thinking
C:am thinking
D:will think
已知函数fx=ln(21-x+a)(a为常数)是奇函数,则实数a为( )
全国多地、多日曾出现雾霾天气,致使空气中PM2.5严重超标.部分PM2.5颗粒能通过呼吸道和肺进入血液,危害人体健康.PM2.5颗粒经过鼻、咽、喉以后,进入血液之前,经过的结构依次是( )