What can block light by placing obstacles in this path , but it much more difficult to block sound why

Which position represents spring in the southern hemisphere? a) b) c) d)

How many protons, electrons, and neutrons are in each of the following isotopes? a. zirconium-90 b. palladium-108 c. bromine-81 d. antimony-123

Why does asexual reproduction result in offspring with identicle genetic variation