Correct Option (3)
: P and T
The city pair P and T provides access to all four specified modes of transport: bus, rail, boat, and air. This comprehensive availability of transport infrastructure between these two cities represents the maximum number of travel options among the given choices.
Incorrect Options:
The other city pairs-Q and S (Option 1), P and R (Option 2), and Q and R (Option 4)-do not offer the complete spectrum of all four transport modes. Consequently, these pairs provide a lesser combination of travel options compared to P and T, and therefore do not represent the maximum available travel choices.