The Question about TO
スラスラと答える
Is the sentence still correct if I delete the TO? If not, I would like to know the reason. I also would like to know when shall I add the TO between a adverb and a verb. Some books say the TO has the grammatical function of emphasis. Is that correct? Thanks in advance!

Question

Answer

You are right. スラスラ答える is correct. But I think スラスラと答える is more formal, and "スラスラ答える" is more casual. If you talk with your friends, you can say "スラスラ言えるよ" or "スラスラ答えられるよ" and stuff like that. But if you write a formal sentence, you should add "と". Four example... "スラスラと答えることが出来ます"
Could you understand ? I would be glad if I could help you. Thank you.