Complete the paragraph. use the correct form of the past simple passive or the present perfect passive. in the first world war, radios ) to communicate with soldiers. since 1960s, many radio signals ) into outer space. so far, no answers ) from other planets. the signals have arrived on other planets, but the massages understand).

In the First World War, radios were used to communicate with soldiers.
Since 1960s, many radio signals have been sent into outer space.
So far, no answers have been received from other planets.
The signals have arrived on other planets, but the massages have not understood.