Pick one

• 1Choice 1.

  Public key crypto is tens to thousands of times slower than symmetric crypto and limited in how much data it handles at once, so the expensive operation covers the small key exchange and bulk data goes through the fast symmetric cipher

• 2Choice 2.

  The server can't decrypt data encrypted with RSA, so a symmetric key is required

• 3Choice 3.

  Symmetric ciphers are mathematically safer than public key ciphers, so the real data uses a symmetric cipher

• 4Choice 4.

  Because iOS's URLSession doesn't support RSA body encryption