Grammar Review, 「げんき」の第5課、 〜てもいいですか、〜てもいい

If we take the 〜て form of a verb and add 〜もいいですか to it or add 〜もいい while asking about something with rising intonation, we're asking whether it's okay to [verb].

窓を開けてもいいですか。/ 窓を開けてもいい?
→ Is it okay if I open the window?

If we drop the question marker か or say the sentence without rising intonation which a question would use, the sentence becomes a statement and we're letting people know that it's okay to [verb].

はい、開けてもいいです。 / ええ、開けてもいい。
→ Yes, it's okay to open it. / Yeah, it's okay to open it.