Chrystal, a support manager at QC Training, is logging into the company's exam voucher application to help a student schedule their required exam. Even though she is already connected to the corporate network, the application asks her to validate her identity by sending her a one$-$time code on her smartphone that she enters to validate her identity. Which of the following security concepts is being utilized by the company's architecture?

A$.$

Gap Analysis

B$.$

Zero trust

C$.$

Hardening

D$.$

Root of trust