$21.$ Last week Ngoc's friend was met by her there.

- S + have/ has + been  V (Pii) + (by O).

$22.$ At the moment rice is being cooked by Tran in the kitchen.

- S + is/ are + being +  V (Pii) + (by O).

$23.$ Next month a prize will be won by Ai Nhi.

- S + will + be + V (Pii) + (by O).

$24.$ To Quyen's exercise is being done by her now.

- S + is/ are + being +  V (Pii) + (by O).

$25.$ Thien Son's clothes were being washed by him then.

- S + were/ was + being +  V (Pii) + (by O).

$26.$ In Ho Chi Minh City a lot of interesting places were seen by Yen Phi.

- S + was/ were+ V (Pii) + (by O).

$27.$ In Tay Ninh a cable car was taken up to the mountain by Tuong Linh.

- S + was/ were+ V (Pii) + (by O).

$28.$ Some vegetables are being peeled by Nhu now.

$29.$ Some books in the library were borrowed by Hai Tam.

- S + was/ were + V (Pii) + (by O).

$30.$ The stain on the table has been erased by My Van.

- S + have/ has + been  V (Pii) + (by O).