清洗内壁沾附碱性固体残留物试管的合理步骤是（   ）

已知倾斜角为θ的直线，与直线x﹣3y+1=0垂直，则tanθ=（　　）

某一批花生种子，如果每1粒发芽的概率为，那么播下3粒种子恰有2粒发芽的概率是(  )

用方框中所给单词的适当形式填空，使短文通顺、正确、连贯（每个单词限用一次）。                                  

get,  look,  some,  year,  a,  write,  by,  tomorrow,  work,  other

      Tommy is a schoolboy. He's thirteen ____  old. He's in Class 3, Grade 1. He always____  up early and he often goes to school ____ bike. He likes English, Chinese and some ____ subjects. He enjoys singing and dancing. But now he is having ____ English class.____ ! some of the students are reading books and some of the students are____  the new words. They are ____  hard . But ____  is Saturday. They don't have ____ classes. He and his friends will go to the movies. I think they'll have fun.

下列有关发达国家与发展中国家的说法错误的是（  ）