As You Operate a Small Table-Top Centrifuge, It Begins to Vibrate

As you operate a small table-top centrifuge, it begins to vibrate and make a noise. This indicates that: (check all that apply)
i. the centrifuge is operating normally
ii. the centrifuge needs calibration
iii. the centrifuge is not properly balanced.
iv. a tube may have broken in the centrifuge.

A) i and ii
B) iii and iv
C) i and iii
D) ii and iii