Put the verb in brackets in the correct tense.
1. It would take about 3 hours to get from Moscow to Leningrad if the train
speed (to be) 300 kph.
2. Switching operations would have been performed with greater difficulties
if the diesel locomotive (not to be) designed.
3. If the refrigerator cars had not been devised, the conveyance of goods for
long distances (not to be) possible.