他們正在挖一個洞。

They're digging a hole.

Source: Tatoeba

Sentence Composition

1 他們 tāmen they; them
2 正在 zhèngzài to be in the process of (doing sth); to be currently ...-ing
3 挖 wā
  1. to dig
  2. to excavate
  3. to scoop out
=4 一個 yīge
  1. a; an; one
  2. the whole (afternoon, summer vacation etc)
=4 一個 yīgè
  1. Combination of the numeral 一 (“one”) and the generic classifier 個／个: a; an; one
  2. same
=5 洞 dòng
  1. cave
  2. hole
  3. zero (unambiguous spoken form when spelling out numbers)

classifier: 個
=5 洞 tóng used in 洪洞 Hóngtóng, a county in Shanxi