What is the principal part of the underlined verb in the sentence?

so far, i have read 10 books this summer.

a.
past participle

b.
present participle

c.
past

d.
present

Plz change it i can not change this sentences .

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.

"she is his achilles' heel" is an example question 3 options: a allusion b alliteration c simile d personification