$1.$ Is RC$4$ a symmetric or asymmetric, block or stream cipher? Why is it popular? And why does NIST still want to define a new standard $($AES$)?$

$2.$ List two major problems of RC$4$ and how to address them?

$3.$ What is the most popular public$-$key algorithm and what are its unique properties?

$4.$ Under what situations should three classes algorithms be used: hashes, symmetric, and asymmetric, respectively?

$5.$ Describe one example where public$-$key algorithm can be used together with the symmetric$-$key algorithm? Why do you think the combination makes sense?