Deuteronomy 10:2

And I will write … which thou brakest So exactly Exodus 34:1 b, E; cp. above Deuteronomy 5:22, and tables of the covenant, Deuteronomy 9:9; Deuteronomy 9:11.

and thou shalt put them in the ark Not now in E for the reasons given above. Hence D's name, the ark of the covenant. See above on p. 64. For the same reason P calls the tables the tables of, and the Ark the Ark of, the testimony.