The first letter stands for the prefix, Kilo, Hecto, Deca, deci, centi, milli, nanno, pico micro. The second letter stands for the type of measure: meter, gram, liter, second. If there is only one letter, it's the type of measure. This should cover most of the following.
-mm. millimeter
-pL. picoliter
-dL. deciliter
-µs. microsecond
-km. kilometer
-m. meter
-ng. nanogram
-Decaliter answer = DL
-Picoampere. pA
-Hectogram. Hg
-Millimole. mMol
-Kilometer. Km
-Megasecond. Ms
-Microsecond µs
-Kelvin K
-Centigram. cg
-Microampere. µa