Both routers must use the same password for CHAP to authentication.
Point-to-point leased line is the most expensive interconnection between two ends as the line is dedicated to a single user, the user should still pay for all available bandwidth, including those unused. -> A is not correct.
With the cost of point-to-point leased line, the full-mesh capability is only achieved when your company has very very strong budget to pay all the bills. To create a full-mesh topology for n sites, we need n*(n-1)/2 leased line connections. For example if we have 6 sites then we need 6*5/2 = 15 leased line connections -> It is nearly impossible for a normal company to achieve full-mesh topology -> B is not correct.
Therefore there are only two available answers left which are correct.
Point-to-point leased line simplifies the configuration as the circuit is available on a permanent basis and does not require a connection to be set up before traffic is passed. It does not require to define a permanent virtual circuit (PVC) in the configuration either -> D is correct.
In fact flexibility is not an advantage of leased line connection so if this question only has 4 options as above then maybe we should choose this.