Why do i need a flu shot every year, while many other vaccinations last years or even a lifetime?

b. the carbon cycle ensures living things have a source of hydrogen

the "power" of a lens is its resolution power, or its ability to distinguish between to closely located points. with the low power lens, it is likely you will see the rough form of the hay and maybe some movement of dots around the hay. however, when observed with the high power lens, the detailed features of the hay become visible and the microbes being grown are more clearly visible.

i hope this you