【单选题】— Do you know if he ______ to play basketball with us? — I think he will come if he ______ free. [ ]
【单选题】---Do you know if he ___to our party? ---I think he will if he ___free tomorrow.
【单选题】图3—9中,当开关S打开瞬间,a,b两点的电位关系是( )。
【简答题】用于人工主动免疫的疫苗有________________、_____________、___________、__________和_____________。