All present-day cells are believed to have evolved from an ancestral cell that existed more than ________ years ago.
举一反三
- The first primitive man known to have existed in China is ( ), who lived about 1.7 million years ago. ( ),who existed more than 600,000 years ago at Zhoukoudian, in the vicinity of modern Beijing, could walk upright, make and use simple tools, and make use of ( ) .
- When was the day named after Valentine? A: More than 1700 years ago before Valentine's death B: More than 2000 years ago C: On February 24 D: It is not mentioned in the passage.
- Children have taken over ______. A: only in America and at present B: more than in America and at present C: more than in America and all the time D: only in America and all the time
- Cell therapies are more complicated than drugs, and hES cells, which have the potential to become any cell type in the body, carry special risks.
- Pride and Prejudice was published _______________. A: more than 200 years ago B: 200 years ago C: less than 200 years ago D: nobody knows