The most accurate summary of the work of archaeologists in the Indus Valley is:
Continual work over many centuries in Indus Valley ruins yielded clues to the civilization.
This response reflects the ongoing nature of archaeological research in the region, emphasizing the gradual accumulation of knowledge about the Indus Valley civilization. The other options contain inaccuracies, such as the specific time periods mentioned and the reference to deciphering the writing, which remains largely undeciphered.