The correct answer is option 4: Over the North Pole. This is because the North Pole is the most direct route from Moscow to San Francisco in terms of distance. When traveling over the North Pole, the distance between the two cities is significantly shorter compared to the other options. Option 1, via Canada, would involve a longer route due to having to cross the Atlantic Ocean. Option 2, overland, would require traveling a long way around continents and bodies of water, making it a much longer route. Option 3, Over the South Pole, would also result in a longer distance as it would involve crossing over the southern hemisphere and additional landmasses. Therefore, the shortest and most direct route from Moscow to San Francisco is to travel over the North Pole.