….. are buying many books at the moment. A Doni and Siti B Siti C She D Doni

….. are buying many books at the moment. A Doni and Siti B Siti C She D Doni

A.Doni and Siti
Doni and Siti are buying many boooks at the moment

Penjelasan :
Karena disitu terdapat to be “are” jadi subject nya harus we,they,you. doni and siti termasuk they. penggunaan lebih dari satu disebut juga they.

jika, hanya siti atau hanya doni ataupun she itu pake nya is, karena tunggal