Question

________ is a type of attack in which the attacker takes control of a session between two machines and masquerades as one of them.

Answer 1

MITM (=Man In The Middle). Even cryptographically secure key exchange algorithms are not safe against a MITM. To prevent MITM, both sides have to have some secret by which they can prove they're 'real', or you need an external trusted party (like a certificate authority) that can vouch for them.