Using the verb DO (or DID) for emphasis
If you want to reinforce, or emphasize, a verb, you can put the (v)DO before it.
The (v)DO is a helping verb. Remember, a helping verb does the work, so that the main verb can be lazy.
The (v)DO will change tense depending on the meaning of the sentence.
The (v)DO needs to agree with the SUBJECT of the sentence.
Because a helping verb always does all the work, the main verb takes the base form.
A: Cris has a lot of friends.
(After A said this, Cris arrived with 10 friends.)
B: Wow! Cris does have a lot of friends.
See TV commercial example: However, you did lie.
This is stronger than saying: However, you lied.
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