A．Discovering the true nature of subatomic particles.
B．Their explanation of the laws of cause and effect.
C．Their work on very high frequency radio waves.
D．Laying the foundations of modero mathematics.
A．To have a three-week holiday.
B．To spend his remaining years.
C．To patent his inventions.
D．To teach at a university.
A．The injury of some students.
B．A school bus crash on the way.
C．The collapse of a school building.
D．A fire that broke out on a school campus.