To marks direction or an infinitive. Too means also or more than enough. Two is the number. Went to the test. Too tired. Two sections. Diction as a set is in word choice.
Also, extra, or a destination
If you can swap in also or excessively, the word is too. If a verb follows, it is usually to: to finish. The number two almost never appears as a diction trap on the ACT; the live pair is to versus too.
Their versus there versus they're is the same kind of look-alike, in their versus there versus they're. Then versus than is in then versus than. Grammar overall is in ACT grammar rules.
The bottom line
Direction or infinitive: to. Also or excessively: too.
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