This is the 33rd most frequent Polish word.
mogą
"They can"
In this sentence, 'mogą' is used to express ability or permission for the subject ('they') to perform the action ('go for a walk').
Oni mogą iść na spacer.
They can go for a walk.
In this question, 'mogą' conveys a speculation or doubtful possibility about the subject being at home.
Czy oni mogą być w domu?
Could they be at home?
Here, 'mogą' indicates possibility or potential of the situation described (the flowers possibly having a beautiful smell).