47. Than and Then
Than is used with comparisons, as in bigger than. Then means at that time, or next.
48. Their and There
Their means belonging to them. There means in that place (as distinct from here). The students left their books there.
49. Who’s and Whose
Who’s is a contraction of who is, as in “Who’s on third?” Whose is the possessive case of who or which, as in “Whose broad stripes and bright stars….”
People often say “very unique,” but strictly speaking nothing is very unique. Something is either unique, which means one of a kind, or not — there aren’t degrees of uniqueness.