2. Observe Why would it
be difficult to sift the iron
filings from the sand?

It is difficult to sieve the iron

filings from the sand because iron filling and sand particles are of the same size. So this method of removal of iron fillings from the sand is not useful. For removing iron fillings from the sand particles, we use magnetic force for it. When a magnet is placed near the sand having iron filling, they attract the iron filling toward itself. So for this, magnets are the best.

the answer to your question is:

c. complementary base-pairing

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