Which sentence uses the underlined word to mean take up a weapon? The underlined word is arm.

he grabbed a stick to arm himself against the threat

theo works for the marketing arm of the company

which arm of the hospital contains the x-ray machines

college had a bruise on her arm from the fall

A?

correct (all the others are not even verbs)

thank u

Yes, sentence A uses the word "arm" to mean take up a weapon. This sentence, "He grabbed a stick to arm himself against the threat," indicates that the person picked up a stick in order to equip himself with a weapon to protect against the threat.