A giant planet is any massive planet. They are usually primarily composed of low-boiling-point materials (gases or ices), rather than rock or other solid matter, but massive solid planets can also exist. There are four known giant planets in the Solar System: Jupiter, Saturn, Uranus and Neptune. Many extrasolar giant planets have been identified orbiting other stars.

Choose your answer: based on the paragraph above can we conclude that "There are many unknown giant planets. "?

Available choices:
[a]. Yes
[b]. It's impossible to say
[c]. No
I think the answer is
[b].