Read the text and complete the sentences with the right prepositions. Answer the question below the text.
Choose the correct option.
One of the first modern searches for extraterrestrial life took place in August 1924, when astronomer David Peck Todd and an inventor Charles Jenkins insisted [on|for|to|of] listening for messages from Mars.
Charles Jenkins created a device, capable of creating visual records of radio phenomena on a long strip of photographic paper. Any incoming signal would trigger a flash of light on the paper, creating black waveform-like lines and thus revealing any chatter of alien radio waves. The Army and Navy proceeded to silence radioactivity for short periods over the three days of Mars's closest course, believing that it could help to track down extraterrestrial signals. Jenkins assured people [about|to|of|on] the successful experiment.
When the paper was developed, the researchers were surprised to find that it contained images. The scientific community complained [on|about|to|for] the experiment failure. They gave logical explanations for these images on paper: these sounds could be static discharge from a passing trolley car, malfunctioning radio equipment, or the natural symphonic radio waves produced by Jupiter. David Peck Todd and Charles Jenkins did not admit [about|for|to|on] believing these explanations.
Write one number in a gap.
How did the researchers want to know about life on Mars?
They wanted to sweep the skies.
They wanted to take pictures of Mars on photographic paper.
They wanted to pick up the signals of extraterrestrial communication.
Answer: [ ]