—Come on, Sandy. Everybody will be lucky or ____(成功的) sometime in their life.
—Thanks, I'll try again.
①试管内液面上升 ②试管内液面不上升
③试管内溶液变红 ④试管内溶液变蓝.
树立健全的环境意识,必须( )①掌握环境科学知识 ②树立正确的环境价值观 ③实现人与自然和谐相处 ④理解、接受并遵守环境伦理原则和相关的行为规范
过抛物线C:y2=4x的焦点F作直线l将抛物线C于A、B,若|AF|=4|BF|,则直线l的斜率是____.