"Cerrar la puerta" can also mean "lock the door". I had written that at first but then I looked at the suggestions and it wasn't there so I put "close the door" instead, I didn't want to lose a heart <3. I think "lock the door" should be accepted. I will report it.
Is "cerrar" also used for the concepts like a business closing for the day or closing for good?
Yep, you say "Cerrar el negocio" to close the business for a day or forever.
Is "closing the door" also a valid expression to describe a window of opportunity ending?
Con esta pronunciación también se podría decir "No voy a cerrar la puerta" (I am not going to saw the door)
I think you meant serrar? Yes, the seseo is pretty annoying sometimes. :´)
Marvy and Cattle: I speak Tagalog (Filipino) and a lot of the words that we use are Spanish or have Spanish Roots. ;)
It's no wonder that Mavry has never heard of "pintô" as a Spanish word for "door". Because it is not. The fact that quite a lot of Filipino words have Spanish origin doesn't necessarilly have to mean that "pintô" (Tagalog word for door) is one of them. It's of Malay origin. Some dialects of Filipino (the language) and some of the other languages of the Philippines, though, do have "pwerta" (from Spanish puerta) and "puerta" to mean "door". Tagalog is not the official language, Filipino is, and "Pintô" is a Tagalog word. And no, it is not Spanish, not even remotely so.
Cool. No, pinto is not door in standard Spanish. As Mavry pointed out, that doesn't rule out the possibility that some Spanish speaker somewhere calls doors pintos, but it does mean that other Spanish speakers will be confused.
No entiendo que demonios es Pintos?-?? diganme quien le dice así a una puerta
I deplore the fact that Duolingo only accepts USA English answers, ie: I am going to close the door (both British and USA English). Also acceptable: I will close the door (USA) since we have no indication that is a "near" future, and I shall close the door - brilliantly British English still spoken by a great number of people, that I know of.