11.   Many experts question its biological activity and consider it a placebo, working in some men who are physically able to have erections because the men believe it will.

12.   Once returned to Earth, the materials will be examined for signs of biological activity.

13.   Researchers would examine the soil and rock for signs of biological activity.

14.   Since the biological activity of naproxen is like that of aspirin and ibuprofen, it is reasonable to assume that it too will protect against heart attacks.

15.   Such compounds readily release oxygen when they encounter moisture, in some ways mimicking biological activity.

16.   The British team said the ratios of carbon isotopes in the rock strongly point to biological activity.

17.   The resulting gusher of carbon dioxide looked so much like biological activity that Gilbert Levin, who devised the experiment, prepared to pop a bottle of champagne.

18.   The two Viking landers conducted life-detection experiments, but failed to detect any indisputable signs of biological activity.

19.   A detailed comparison of the soils showed that the organic fields had more biological activity and biomass, both signs of soil health, than did the conventional fields.

20.   But researchers have found it tricky to get the proteins to stick to the membrane without losing their biological activity.