1.They gave my village tonnes of rice three days after the earthquake. (Passive voice)
=>  my village was given tonnes of rice three days after the earthquake
2.The government will send rescue workers to flooded regions tomorrow. (Passive voice)
=> rescue workers will be sent to  flooded regions by the government tomorrow.
3.People use too much herbicides to treat weeds. Water in rivers, canals, lakes are extremely polluted and has bad effects on people's health. (because)
=>. Water in rivers, canals, lakes are extremely polluted and has bad effects on people's health because people use too much herbicides to treat weeds
4.I don't have enough time.so I won't take part in the volunteer programme. (If)
=>. if i had enough time, i would  take part in the volunteer programme
5.She doesn't know my address, so she can't write to me. (If)
=> if she knew my address, she could write to me
6.My advice is that you should spend time doing outdoor activities. (If)
=> if i were you , i would spend time doing outdoor activities.