Question

change the verbs in brackets into the passive and complete the sentences.(1) the sahara was not always a desert millions of years ago_________(cover) in grasslands and forests. now, only a tenth of the sahara desert____________(cover)with wind-blown sand. the rest is plains and mountains.(2) many stars in the universe are bigger than our sun. the biggest star__________(estimate) to be over 700 times as big as the sun. so, these stars________(know) as blue giants.

Answer 1

The sahara was not always a desert  millions of years ago.   
It was covered in grass lands and forests.    
Now, only a tenth of the Sahara desert is covered with wind-blown sand.
The rest is plains and mountains.

Many stars in the universe are bigger than our Sun.
The biggest star is estimated to be over 700 times as big as our Sun.
So, these stars are known as blue giants.