Could we use both museums and musea? Dutch seems to have a lot of words borrowed from Latin
Probably musea. For most words ending in -um derived from Latin, the -a used to be the only correct plural form, but recently this has changed, basically because people were using the -ums form (sometimes language is very democratic). Other examples of -um words are centrum, decennium and lustrum.
Octopus is derived from Greek, not from Latin. The correct plural (in English) is octopodes, although octopi and octopuses are both more commonly used.
You SHOULD say musea in plural. Een museum, Twee musea. One museum, two museums.
As far as I know, only the nouns ended with a, i, o, u, y would have the plural form -'s.
Why is "in front of" not correct for "voor"? It's one of the choices and makes sense since some museums do collect before you enter...
Couldn't be this sentence translated as a promise? If yes we could use future simple as well as present tenses here. I did that and Duolingo didn't accept it
No this sentence is just a statement. If you want to make it a promise you would use "zal betalen".
Just like in English then ; I shall pay ( Ik zal betalen ). Correct me if I'm wrong
Het museum / de museums... is this a general rule for het / de? Are plural words always de? Someone please remind me of the rule