This is the 6547th most frequent Chinese word.
於在
"於在" is not a standard or common Chinese phrase. It may be a combination of "於" (in/at/on) and "在" (to be located at/in), but together they lack a clear, standalone definition.
In this sentence, '於在' emphasizes the location or subject of focus, '集中於在那本书上', where the usage is somewhat redundant or stylistic.
他所有的注意力都集中於在那本书上。
All his attention is focused on that book.
Here, '於在' indicates the location being described, '於在北方', demonstrating its use to specify a context.
於在北方，冬季的气候通常比较寒冷。
In the north, the winter climate is usually colder.
In this instance, '於在' ('於' and '在' combined) is used to introduce the situational context, '於在大多数情况下', where it specifies the situation of the statement.