If you had a trapped gas and continued to cool it until the lowest possible temperature is reached, this temperature is called check all that apply.
a. 0 k.
b. -273
c.
c. absolute zero.
d. zero temperature.

Welll . . . . . Here we must call in Ms. Serena Semantic to make
a judgement call for us.

You said the "lowest possible temperature", and that could mean
two different things. 

-- It might mean the lowest temperature allowed by the laws of Physics,
at which all molecular motion ceases, and no thermal energy exists.
OR
-- It might mean the lowest temperature that has so far been achieved
in the laboratory ... the lowest currently possible for Scientists.

The first one ... the lowest temperature allowed by the laws of Physics,
is called zero Kelvin, or -273.16 °Celsius, or Absolute Zero.

That temperature has never been achieved in the laboratory, and there
are good reasons why it never CAN be.

In 2003, a team at MIT cooled a sample of gas to the temperature
of one half-billionth of 1 Kelvin.  That was pretty cold, but it wasn't
Absolute Zero.