Problem:

$1.$ Consider the following argument:

"The Russians will accept our proposal for banning chemical warfare only if we drop our demand for on$-$site inspections. The US will drop that demand if and only if we believe everything the Russians tells us$.$ We will not believe everything the Russians tell us unless we are incredibly naive and they accept our proposal. So$,$ if we are incredibly naive and drop our demand for on$-$site inspections, the Russians will accept our proposal for banning chemical warfare." $($Key for Basic Propositions: A$,$ D$,$ B$,$ N$)$

$2.$ Identify the correct $($or best$)$ formalization and proof of validity for the correct$/$best standard$/$linear format re$-$representation.

UPDATE: There is a typo in the answers. The conclusion of each proof below should be $($N&D$)->$A$.$ Blackboard is$,$ for some reason, not optimized well enough to enable me to change the answers themselves.$$

$1.$

Like the other proof from five premises but with Modus Ponens instead of Conditional Proof.$$

$2.$

$3.$

$4.$

Like the other proof from three premises but with Modus Ponens instead of Conditional Proof.$$

$5.$

Like the other proof from four premises but with Modus Ponens instead of Conditional Proof.$$

$6.$