Final answer:
The men suppose that Lennie stole Carlson's gun and ran off with it. However, this is hard to believe because Lennie is not capable of such actions.
Step-by-step explanation:
The men suppose that option a) Lennie stole Carlson's gun and ran off with it. This is hard to believe because Lennie is not capable of such actions. The evidence from the text suggests that Lennie is mentally disabled and does not have the capacity to plan or carry out theft. It is unlikely that he would be able to successfully steal and escape with a gun without anyone noticing. Therefore, this explanation is not plausible.