Please break this down into S and N and indicate the conditionals

I think the critics thing for SN is to remember it's just a guarantee: a sufficient condition guarantees the necessary condition is also true, so let's look for those relationships. The first sentence tells us that large cities needed large farms nearby. So, If LC then LF The second tells us that foraging and other methods of food production can't support cities. This means that if we have cities, it's guaranteed we don't only have foraging. This is just restating the first idea, that if cities then farming. Next we are told that large farms require irrigation, so If LF then I. Finally we are told that this isn't possible in arid areas until recently so in premodern times If I then near water source Or If large cities then large farms, then Irrigation, then near rivers or lakes (if not modern times).