We haven't known ____ there is life on Mars.A.that B.if C.wh

We haven't known ____ there is life on Mars.A.that B.if C.wh Is there life on Mars(火星)?We do not know.We are sure that ea if it ____,we won't go there.A rains B will rain C is rainin 1.There is no ____ on Mars,____ is known to all. NOVA IS THERE LIFE ON MARS怎么样 On Mars,there is no pollution ___ by traffic.A is caused B c ____ i will go out depend on the weather.A If B Whether C wh Most scientists believe that there is no life on Mars as c__ Starting with the ___ that there is life on the planet Mars, I don't know ____ they have passed the exam.A.what B.if C.wh This is ____ that we mustn't waste time A what B because C w Bamboo is hollow,____ makes them very light.A.that B.it C.wh