@Hossam6,
In such case answer the guest within the 24 hours time-limit and do nothing more. It is not obliged to decline or pre-approve an INQUIRY, just remove it from your dashboard. Your responsrate is in your account, section "progress". If you decline very often, especcially on REQUESTS, which must be accepted or declined, it will affect your rating and your position in the search results.
BTW If a REQUEST is only a question (so the guests should have sent an INQUIRY instead) or can not be fulfilled because the guest did not read the listing correctly, ask the guest to withdraw it within the time-limit, so it saves you a decline because of the guest being in error.
Hope this helps,
Emiel