A.to show chemical batteries are widely applied. |
B.to introduce nuclear batteries can be safely used. |
C.to describe a nuclear-powered system. |
D.to introduce various energy sources. |
A.uses a solid semiconductor |
B.will soon replace the present ones. |
C.could be extremely thin |
D.has passed the final test. |
A.science news report | B.book review |
C.newspaper ad | D.science fiction |