"Hun klantenservice is de beste."
Translation:Their customer service is the best.
why is there an 'e' affixed to 'best' if that adjective is not followed by a noun?
"Het best" should also be accepted. With "de beste", those words refer back to the noun directly, and imply the noun so that it doesn't need repeating. The closest English construction would be "the best one" (which isn't accepted as a translation but should be).
As a native Dutch speaker I can tell you that 'het best' is not grammatically correct, 'het beste' is correct. I suck at grammar rules, so I'm hoping somebody else can explain that part to us :-)
I disagree as a native speaker. "Hun klantenservice is het best." is also correct.