3:
Depends on the type of slow. But generally for CC (except knockups) there's Tenacity which you get from either Mercury threads
(most common), Zephyr
, jungler Item enchant Juggernaut (green enchant)
or Elixir of Iron
. You can also get it from the ultimate defensive mastery.
Tenacity reduces the duration of any crowd control effects that gets stuck on you, which makes it great for lessening stuns, snares, silences, blinds, and basically every form of Crowd Control effect but knockups.
If you're facing a lot of easily reapplied slows (like Ashe's
frost shot, which slows you every time her arrows hit) or slow fields (Like Lux's
Lucent Singularity, which slows you while you're in the area). You may instead consider effects which lessens the strength of the slow.
The only readily availible source of anything like this that I know of is Boots of Swiftness
which is faster than all the other combat apliccable boot upgrades and also decreases the effect (not duration, but how strongly you're slowed) of slows specifically. These of course does not apply on other forrms of CC.
If you're facing a few or even several powerful effects, there's Quicksilver Sash
and it's upgrade Mercurial Scimitar
which both feature an active component which removes most if not all forms of debuffs on you at the moment of activation.
There's also Mikael's Crucible
which has an active which heals one friendly champion and removes most of the common forms of CC from them aswell. It's not as thorough as Quicksilver/Mercurial, but might be easier to fit into the build of some champions (and can be used to help teammates as well as yourself.
If you want to come extra prepared there's the summoner spell Cleanse
Which removes most (but not all) forms of CC and lowers duration of any which hits you the next couple of seconds.
And that's all I can think of. But i'm still relatively new at this game, so I probably missed out something or other. (I for one didn't go into champions specific abilities because I know less than a third of the champions well enough to have an idea of what their kit does.)
Hope this is a help, or at least not too annoying.