if they themselves participated in or saw the event take place, it's a primary source.
if they HEARD it from someone who participated/saw the event, it's secondhand information, and therefore a secondary source.
The three main sources of oxygen are photosynthesis by plants and algae, oxygen released during the breakdown of water molecules, and oxygen produced by phytoplankton in the oceans.
During coal burning, carbon dioxide is produced as a byproduct. This is a type of greenhouse gas that contributes to climate change.
The main sources of the world's natural gas are from underground deposits in sedimentary rocks, such as shale formations, and from associated gas produced during oil extraction.
A primary source is a document, speech, or other sort of evidence written, created or otherwise produced during the time under study. Secondary sources provide interpretation and analysis of primary sources.
According to Honda and other sources, there were a total of 18,865 NSX's produced worldwide during its entire production run (1990-2005).
The sources of variation in offspring produced by sexual reproduction include genetic recombination through meiosis, independent assortment of chromosomes, crossing over during prophase I, and random fertilization of gametes leading to a unique combination of genetic material.
The energy sources needed for the light reactions in photosynthesis are light (photons), which are absorbed by chlorophyll. The energy sources needed for the carbon reactions (Calvin cycle) are ATP and NADPH, which are produced during the light reactions.
Disk throwing
During fasting the glucose is relaesed from intracellular glycogen stores in the liver (produced by glucogenolysis). After a meal blood glucose is acquired from the diet.
United states and Great Britain
Which gulf war. The US participated in three of them.
Yes, carbon dioxide (CO2) is produced as a byproduct during fermentation.