On a communication line, the velocity of propagation is $100000$

m$/$s$,$ its length is $10$ km and the data rate is $1000$ Mbps$.$ Using circuit

switching technology, the number of bits that should be transmitted in

a time slot to achieve a line efficiency of $90\%$ is:

$($a$)1800($b$)18($c$)10000($d$)$ neither a not b nor c