<prompt> An OPV vial shows this symbol on it. What does it indicate?The vaccine has reached its expiry dateThe vaccine has not been stored properlyThe vaccine vial is emptyUse the vaccine if expiry date not reached  <response>: d. Use the vaccine if expiry date not reachedThis is a vaccine vial monitor VVM showing white inner square blue outer circle; VVM provides an indication of the cumulative heat to which the vial has been exposed 