Question

the trenches were grimy because they were dirty, old, deep, dirty, long

Explanation:

To solve this, we analyze the meaning of "grimy", which means dirty or covered in grime. Among the options, "dirty" is the synonym that fits the context of explaining why the trenches were grimy. "Old", "deep", and "long" don't relate to the meaning of grimy.

Answer:

dirty (the option corresponding to the word "dirty" in the dropdown, as it is the synonym of "grimy" and logically explains why the trenches were grimy)