The correct option is
B or
The given sentence needs to be filled with the most suitable conjunction. The words 'you can fly', 'you can ride the ferry' are both alternatives. Hence, we need a conjunction that can combine the two alternative clauses in one sentence.
Option D is correct - 'To go from Mumbai to Goa, you can fly, or you can ride the ferry.' 'Or' is a conjunction, which is used to combine the alternatives.
Option A is incorrect, as 'and' is used to connect two clauses in a sentence. Here, we can't say -'You can fly and you can ride the ferry', because travelling can't be done in two ways at a time. The sentence has alternative ideas/options and needs a coordination conjunction to combine them.
Option B is incorrect, as 'but' is used to express excuses and contrasting clauses in a sentence. As the sentence doesn't have contrasting ideas or clauses, we can't use 'but' here.
Option C is incorrect, as 'so' is used to express reasons. The sentence has two alternative ways to travel to Goa, hence, we need 'or' to combine these alternatives.