The viola strings are CGDA. Notice that it is tuned in fifths, CdefGabcDefgA.
Counting the C, there are five notes to the next string.
The bass, cello, viola, and violin are all tuned in fifths.
so is a cello GDAC and then the base at DACG?
The fiddle/violin is usually tuned G-D-A-E, where the G is below middle C on the piano.
A viola is C-G-D-A , The C is one octave below middle C, a perfect fifth below the violin. The G-D-A strings on a violin and a viola are the same, in the same octave.
A cello is tuned, low to high, C-G-D-A, the same as a viola but an octave lower. The C is two octaves below middle C on a piano.
Double basses are usually tuned in fourths, low to high, E-A-D-G, which is one octave lower than the four lowest-pitch strings on a guitar. That's the lowest E on a piano.