(A) made or declared or believed to be holy
(B) a politically organized body of people under a government
(C) experimentation to determine how well something works
(D) ** in or at this place; where the speaker or writer is
EXPLANATIONS BELOW
Concept note-1: -“In” for Location. Deciding which word you should be using comes down to a question of where. “At” is used when you are at the top, bottom or end of something; at a specific address; at a general location; and at a point. “In” is used in a space, small vehicle, water, neighborhood, city and country.
Concept note-2: -Yes, your statement was perfectly grammatical. Your customer is correct that you don’t have to say ‘at’: “where it is” is every bit as acceptable as-and in some circumstances more acceptable than-“where it’s at”, but “where it’s at” is not ungrammatical as such.
Concept note-3: -“At my place” is the most correct.
Concept note-4: -The main difference between in and at is their specificity. The preposition in is mostly used with less specific times and locations whereas at is used with specific times and places. In addition, there are also other specific uses for these two prepositions, which cannot be interchanged.