Visual mixing is often associated with the post-Impressionist era of the late nineteenth century and can be observed in the works of artists such as Seurat and van Gogh. The techniques of and both use small bits of juxtaposed color to produce different color sensations.

productive most commonly means: achieving or producing a significant amount or result.

explanation:

productive can also mean:

producing or giving rise torelating to or engaged in the production of goods, crops, or other commodities.

these depend on how the word productive is used. most likely productive will mean   achieving or producing a significant amount or result.

The truth is that any source can be the best source for some kind of research. as an example, if you were to write an essay about the credibility of wikipedia, would you avoid citing wikipedia? clearly not. as we know, the president of the united states jumps on twitter all the time. if you’re writing about trump, what better source can there be? it is, quite literally, an original historical document. the same would be true if you were writing about the events of the moderately recent revolutions in egypt and syria. what better source than someone who is right there in the thick of things? clearly you would have to contextualize the source as at least moderately unverified in most such cases.