A floodlight operating at a point $500$ feet from the meter, wired with #$14$ wire whose resis. tance is $2\mathrm{.}575$ ohms per $1000\text{'},$ has a voltage drop of approximately

A$.5\mathrm{.}7$

B$.11\mathrm{.}33$

C$.12\mathrm{.}74$

D$.15\mathrm{.}37$

The grid in the vacuum tube was introduced by