In the circuit below, R$1=54,R2=105,R3=230,R4=40.$ An ohmmeter is an instrument that gives a value for the resistance seen between two terminals. What is the correct reading if the instrument is attached to the network in the figure given at points: $($a$)$ BC

$($b$)$ BD

$($c$)$ CD $?$

$($a$)R_{BC}=$

$($b$)R_{BD}=$

$($c$)R_{CD}=$