中国大学MOOC: There are some invisible dead stars called black holes.
举一反三
- 中国大学MOOC:"Why do scientists know black holes exist?";
- 中国大学MOOC:"You cannot imagine how fantastic the sky was with the stars __________ in the black velvet of the night. (twinkle)";
- 中国大学MOOC: The sky is clear; the stars are twinkling.
- Most stars are not ______ to the naked eye. A: visit B: visible C: vision D: invisible
- The most______(convince)evidence of black holes comes from research into binary star systems.