If there are sentient beings on planets outside our solar system, we will not be able to determine this anytime in the near future unless some of these beings are at least as intelligent as humans. We will not be able to send spacecraft to planets outside our solar system anytime in the near future, and any sentient being on another planet capable of communicating with us anytime in the near future would have to be at least as intelligent as we are. The argument's conclusion can be properly inferred if which one of the following is assumed? ['Any sentient beings on planets outside our solar system that are at least as intelligent as humans would be capable of communicating with us.', 'If a sentient being on another planet cannot communicate with us, then the only way to detect its existence is by sending a spacecraft to its planet.', 'There are no sentient beings on planets in our solar system other than those on Earth.', "If there is a sentient being on another planet that is as intelligent as humans are, we will not be able to send spacecraft to the being's planet anytime in the near future."]