`1`. David said he thought there were 9 planets in the solar system.
`2`. Tom asked me if I thought aliens from other planet might contact us one day in the future.
`3`. Dean asked Tom how scientists could discover the surface of other planet
`4`. Edward asked his friends when people could travel to the Mars as tourists.
`5`. Nick asked his father if aliens would be friendly to people on Earth
`6`. Tom asked me how many starts there were in our galaxy.
`7`. Dean asked me how long it took a space buggy to travel to Mercury
`8`. Linda asked me how old our Earth was
`9`. Robert said he believed one day in the future aliens might visit the Earth.
`10`. Carlos asked me how they could send message to other planets.
Giải thích: Câu tường thuật lùi thì.