When does a neutron from one atom collides with the nucleus of another atom, a chain react

When does education begin？A．Before one enters school.B．After one enters school.C．After one

听力原文：When does he return from Hong Kong？（A) At home, mostly.（B) Tomorrow, as I know of

When does the new system go into effect？A．Immediately.B．From next week.C．From next month.D

When does the man offer to return？A．In an hourB．In one and a half hourC．In two hoursD．Tomo

When does the driver think they will get there？A．At about 7 : 30B．At about 7 : 25C．At abou

When does education begin？ 查看材料A.Before one enters