This is the weighted average of all of the isotopes of an element.

a. a primary source combines several different accounts of an event. b. a primary source generally benefits from having been written after an event.

explanation:

ljjjljlj kjlk,ljym jlyu; jm; l mumytj

we can conclude that the melting point of table salt is above room temperature (it's actually 801 deg c). the melting point of mercury must be below room temperature (- 39 deg c).