Which mission focused primarily on studying the geological features of the moon?

The Lunar Orbiters were specifically designed to study the geological features of the Moon. These missions, which took place in the mid-1960s, aimed to map the lunar surface in detail, providing critical information about its topography and mineral composition. The data collected by the Lunar Orbiters helped scientists understand the Moon's geology, including its craters, maria (the dark basaltic plains), and other surface features. This information was essential for planning future lunar missions, particularly those that would involve landings and exploration, such as the Apollo missions.

In contrast, the other missions listed had different focal points: the Surveyors were focused on soft landing techniques and conducting surface experiments, the Rangers were primarily tasked with high-resolution imaging of the Moon just before impact, and the Mariners were focused on the exploration of Mars and Venus, rather than the Moon. Thus, the correct choice of the Lunar Orbiters emphasizes their dedicated role in lunar geological study.