Context: On 5 October 1407, the prisoners were charged with high treason by the Ming imperial court. The Yongle Emperor asked them whether they had killed the former king and whether they had usurped the throne of the Trần royal family, but he received no answer in return. In the end, most of these prisoners were either imprisoned or executed. In June 1407, the Yongle Emperor annexed the conquered region as Jiaozhi  province. Lü Yi was appointed as the military commissioner, Huang Zhong as the vice-commissioner, and Huang Fu as the provincial administrator and the surveillance commissioner. Jiaozhi province became divided into fifteen prefectures, 41 sub-prefectures, and 210 counties. The first major signs of discontent against Chinese rule would surface when Tran Ngỗi  revolted in September 1408. Even though he would be captured by Zhang Fu in December 1408, Tran Qui Khoang  would continue the rebellion until his capture by Zhang Fu on 30 March 1414, formally ending the rebellion. Nevertheless, the region would continue to be plagued by several other uprisings during course of the Chinese domination, and the Ming occupation army was eventually evicted out of Vietnam in 1427 as the result of the Lam Sơn uprising. The Ming's ethnic Vietnamese collaborators included Mac Thuy whose grandfather was Mạc Đĩnh Chi who was a direct ancestor of Mạc Đăng Dung.

Question: What did Jiaozhi become the most divided in, prefectures, sub-prefectures or counties?

Answer:
counties