1. Queiro que ustedes hablen español.
Why?
X- Hablan is used for a question, such as: "¿Ustedes hablan español?" ( Do you all speak Spanish? )
X- Hablar is more of a question/ demand. For example: "Ella va hablar" ( She's going to speak ) or "¿Usted va hablar español?" ( Are you going to speak Spanish? )
X- Hablaron is more of a statement. Example: "Ellos hablaron español" ( They spoke spanish. )
2. Prefiero que escribas una carta.
Why?
X- Escribe is a demand. Example: "Escribe una carta." ( Write a letter. )
X- Escribí is a statement. Example: "Yo escribí una carta." ( I wrote a letter. )
X- Escribo is also a statement. Example: "Yo escribo una carta." ( I write a letter. )
3. La agente de viajes recomienda que nosotros llevemos poco equipaje.
X- Llevar is wrong because it doesn't quite fit any sentence, except "Ella va a llevar un poco" ( She's going to take a little bit. )
X- Llevábamos is not a word in spanish.
X- Llevamos is a statement. Example: "Nosotros llevámos un poco." ( We took a little. )
So the answers would be:
1. Hablen
2. Escribas
3. Llevemos
Hope this helps!~
