In both cases you need the reflexive pronoun.
The first is correct. The second is not. What is so small that it passes through very fine filters? Bacteria. "They" refers to bacteria.1)The bacteria are very small.
That's why they pass through very fine filters.
a-The bacteria are so small that they pass through very fine filters
b-The bacteria are so small that pass through very fine filters
The first is correct. The second is not.2)The country has many natural resources.
That's why it can support itself easily.
a-The country has so many natural resources that it can support itself easily.
b-The country has so many natural resources that can support itself
easily
8)
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