$1$. $-->$ How about giving a presentation about water and air pollution ?

$2$. $-->$ There is plentiful water for life on Earth.

$3$. $-->$ By the time I started primary school, I had learnt how to ride a bike

$4$. $-->$ We've decided to stay in Ho Chi Minh City for three days

$5$. $-->$ Scientists are planning to send people to explore Mars in the near future

$6$. $-->$ We had better not throw rubbish on the streets.

$7$. $-->$ Our car will be serviced by a mechanic tomorrow morning.

$8$. $-->$ Have you ever been to an English speaking country?

$9$. $-->$ I made lots of grammatical mistakes in the writing.

$#Vnhee$