Which of the following is used as a moderator in nuclear reactor?

Which of the following is used as a moderator in nuclear reactor?
  A.  Ordinary water
  B.  Radium
  C.  Thorium
  D.  Graphite (Ans-D)
7. In an atomic nucleus, neutrons and protons are held together by
  A.  Gravitational forces
  B.  Magnetic forces
  C.  Exchange forces(Ans-C)
  D.  Coulombic forces
8. Television signal cannot be received generally beyond a particular distance due to
  A.  Curvature of the earth(Ans-A)
  B.  Weakness of antenna
  C.  Weakness of signal
  D.  absorption of signal in air
9. Which one of the following is the unit of activity of a radioactive source?
  A.  Lux
  B.  Becquerel(Ans-B)
  C.  Tesla
  D.  Siemens
10. Which one of the following is a good conductor of electricity?
  A.  Shellac
  B.  Ebonite
  C.  Glass
  D.  Human body(Ans-D)