The major problem with hydrogen as an alternative source of energy is that none exists on the surface of the earth. a. true b. false

Plz will mark! the diagram shows the positions of the sun, moon and earth during spring tides, when the high tides are at their highest and low tides at their lowest. what is it about these positions that causes these high and low tides?

Which worm has eyespots that are used to detect light? a fluke b marine worm c planarian d tapeworm

Which of the following cell structures is significantly different between gram- positive and gram-negative bacteria?