Answer is B.
In circuit switching, a fix bandwidth is allocated to each connection, e.g. $64$ $Kb/s$ allocated to each each phone call.
In circuit switching each connection has a dedicated circuit or channel all the way along the path and the circuit is not shared with anyone else.
Thus in circuit switching each call has its own private, guaranteed, isolated data rate from end to end.So we can say that every connection or flow is independent of others.
In the case of packet switching, all flows share the full channel capacity by statistical multiplexing.
So, the bandwidth allocated to each flow depends upon the number of concurrent flows & network traffic.
In packet switching if we know the type of link we are using, the bandwidth allocated, the packet size for any flow then we can calculate the Propagation Delay & Transmission Delays.
But, Queueing Delay is a random variable that depends upon the number of packets arriving at the same time at any switch.
It is the only random variable in our end to end delay expression.All other delays can be calculated precisely if we have enough information about the flows.
So, queueing adds unpredictable & variable delays in the packet switching.
There are delays like propagation delay etc. in circuit switching but they have a very small variance because of independence, privacy & bandwidth guarantees.
