A. What do you think is the best diet?

B.  The best diet I think is exercising well and eating enough nutrients. ✔​

(04/08/22)

-그들은 소포를 배달했다.

They delivered the packets.

=> Another way: Your sentence is okay and this is another way of saying it.

 They delivered the package.

-버스는 8시 30분에 도착했다.

The bus arrived at 8:30. ✔​

-Jenifer는 나를 그녀의 가장 친한 친구한테 소개했다.

Jennifer introduced me to her best friend. ✔​​