Final answer:
The US used landers and rovers to find out whether the regolith on Mars would be a problem by conducting experiments and analyzing the composition of the soil.
Step-by-step explanation:
The US found out whether the regolith on Mars would be a problem through the use of various landers and rovers. For example, the Viking landers in 1976 carried out experiments to test the composition of the Martian soil and determine if it contained organic material. They also looked for evidence of microorganisms. Later missions, such as Pathfinder, Mars Global Surveyor, and Mars Odyssey, provided further insights into the Martian surface and the presence of water, which is essential for determining regolith characteristics.