High spring tides occur at new moon and full moon because the Sun, Earth, and the Moon are in a straight line.

Let`s dissect the options to understand why this is the correct answer. Option 1 states that the Moon and Earth are at right angles. This would actually result in neap tides, which are lower tides. Option 2 suggests that the Sun and Moon are at right angles. Although the Sun does influence tides, it is not the primary cause of spring tides. Option 4 states that the Sun and Earth are at right angles. This would also result in neap tides, as the gravitational forces from the Sun would partly cancel out the gravitational forces from the Moon.

Therefore, option 3 is the correct answer because the alignment of the Sun, Earth, and the Moon in a straight line creates a stronger gravitational pull, leading to high spring tides. This alignment occurs during the new moon and full moon phases, which is why high spring tides occur during these times.