Sentence 1: I took my son to Europe. 
 Sentence 3: I agreed to take him on a train 
 Sentence 4:  I booked two tickets for a train from Spain to France 
 Sentence 5:  My son had a great time on the train! 
 Option 1: He said he wanted to see Big Ben in London. 
 Option 2: He said he wanted to go on a train.