For the following statements,write $T$ for True and $F$ for False.
$(a)$ $J$.$J$. Thomson proposed that the nucleus of an atom contains only nucleons.
$(b)$ $A$ neutron is formed by an electron and a proton combining together. Therefore,it is neutral.
$(c)$ The mass of an electron is about $\frac{1}{2000}$ times that of a proton.
$(d)$ An isotope of iodine is used for making tincture iodine,which is used as a medicine.

• A
  $(a)-(T); (b)-(F); (c)-(T); (d)-(F)$
• B
  $(a)-(F); (b)-(T); (c)-(T); (d)-(F)$
• C
  $(a)-(F); (b)-(F); (c)-(T); (d)-(F)$
• D
  $(a)-(T); (b)-(F); (c)-(F); (d)-(T)$