Regarding 19:10 and 21:79

[munir rana]

Dear Brother Joseph and  Forum Members
Salam.

I haven't been able to be here for a long time.
Anyway, here I am with some query regarding some verses now, if you can help.

19:10 (Zechariah) said, `My Lord, make for me a sign.' He said, `Your sign is that you will not speak to the people for three nights, (being) sound.'
How can it be a sign? what does a sign mean?
Brother Joseph wrote in a response that `It purely depends on the context'. I agree. But failed to understand this context.

Here is another verse.
21:79 And we gave understanding of the case to Solomon, and to each (of them) we gave judgement and knowledge, and we subjected the mountains to exalt (Us), along with David and (also) the birds. And we were doing.
This was narrated once again in 34:10
What do you understand by `mountains exaltation along with David and birds.'
Thanks and salam to all.