Which two qualities of PKI key exchange overcome asymmetric cryptography scalability issues?

Which two qualities of PKI key exchange overcome asymmetric cryptography scalability issues?
(Choose two.)

A.
the trusted introducer uses the signed certificates of the endpoints that need to communicate

B.
the introducer digitally signs the public key of the user with the public key of the introducer to
generate a signed certificate

C.
only the public key of the introducer has to be initially known and verified by all other entities

D.
pki uses only a single trusted introducer

Explanation:
Chapter 14: Understanding Cryptographic Fundamentals and PKI pg. 374
A PKI does not eliminate the need for authenticity when you exchange public keys in an
asymmetric encryption environment, but it solves the scalability issues associated with that
process.
A PKI uses the concept of a single, trusted introducer. Instead of securely exchanging all public
keys among all devices, only the public key of the trusted introducer has to be securely distributed
to all devices. This exchange is usually done by downloading the public key and then verifying it

out of band.