1.Tom asked the guard  where he could park his car

can--> could 

S + asked(+O)/wanted to know/wondered + Wh-words + S + V.

2. Ann told Tom that he wanted to visit Ho Chi Minh city

hiện tại đơn --> quá khứ đơn

3. Ba asked Lan if she could speak English fluently 

S+asked/wanted to know/wondered+if/wether+S+V

4. The teacher asked Hoa if he was always taking in the dars

hiện tịa tiếp diễn --> quá khứ tiếp diễn

5. The children said they was waiting for the school bus

hiện tịa tiếp diễn --> quá khứ tiếp diễn

6. Liz told me that her mother would  take her to the rice - cooking festival in vietnam that week

will--> would