[___] tides occur when the Sun, the moon, and Earth are nearly aligned. [___] tides happen when the Sun and the moon are at right angles to each other. Each of these special tides happens [___] in a lunar cycle.

The Sun, Moon, and Earth line up during spring tides, while the Sun and Moon are at right angles during neap tides. Each arrangement occurs twice during a lunar cycle, so the correct choice is “twice.”

AI-written and checked against the verified answer.