{"correct_option"=>"b", "explanation"=>"The correct option is 'b. send'. The sentence asks Mr. Jones to perform an action related to a letter. The most logical action is to 'send' the letter to their partners. 'Ask' would be more appropriate if the sentence was referring to a question or if Mr. Jones was asking about a letter, 'receive' would mean that Mr. Jones would get a letter, and 'call' is more suitable if someone was going to make a phone call, not send a letter."}