b. south and are colder at the source than at the mouth
Explanation:
<u>The great Siberian river like the Ob, Yenisei, and Lena all flow to the arctic ocean and thus flows in the east to west direction and has a relatively flat percentage of the landmass. The southern flow makes these rivers more warm as compared to the icy content that it gathers to form the northern sides.
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Within the impact of the winter season, these rover water get thawed and thus re-reach the southern ends with relatively less cold waters as they have a tendency to flow downward. When they are joined form the nearby seas.
