Which words in the sentence are the adverb clause?

whenever our cousin travels, he often visits us later to tell about his adventures.

a.
later to tell about his adventures

b.
he often visits us

c.
about his adventures

d.
whenever our cousin travels

The greatest gift the sumerians gave the world was the invention of writing. the sumerians were wealthy people. they needed some way to keep track of what they owned. they began drawing pictures. they used a reed as a pen. they drew on soft pieces of clay. the soft clay was then dried in the sun. the tablet became a permanent record. later, the sumerian drawings changed into wedge-shaped symbols. this kind of writing is called cuneiform. by putting symbols together, the sumerians could write entire sentences.