Scientific racism<span> (sometimes </span>race biology<span> or </span>racial biology<span> or </span>pseudoscientific racism<span>) is the </span>pseudoscientific<span> study of techniques and hypotheses attempts to reveal the biological differences between races which can be used to support or justify belief in </span>racism<span>, racial inferiority, or </span>racial superiority;<span> alternatively, it is the practice of classifying</span><span> individuals of different </span>phenotypes<span> or </span>genotype<span> into discrete </span>races. Historically it received credence in the scientific community, but is no longer considered scientific.
Fog, the other three options would be too high in the atmosphere to cause visibility problems.
I think that it was at the year of 1619
The group of Muslim Arabs <span>most threatened the Byzantine Empire in 1050</span>