The important achievements of the Kushites among the options provided are:
1. The development of Africa's first iron-working city.
2. Trade networks that stretched from Greece to south of the Sahara.
3. The famous text, The Book of the Dead.
(Note: While the Kushites had a significant cultural influence, they did not invent the alphabet or papyrus, which were more associated with earlier Egyptian civilization. The defeat of the Assyrians was also not a successful achievement since the Assyrians later conquered Kush.)