Explanation

The standard incubation period for common quails (Coturnix coturnix) is typically 16 to 18 days, with 17-18 days being most cited in poultry science. However, many sources specifically state 17 days as the average for Japanese quail, which is the most common breed in agriculture. Wait, let me double check. Common Quail: 17-18 days. Japanese Quail: 16-18 days, often cited as 17 or 18. Some sources say 16 days for certain breeds or conditions. Let's verify standard MCQ databases for Pakistan agricultural exams. Often, '17 days' is the accepted answer in many textbooks (e.g., Poultry Science by various authors). Actually, many sources cite 17-18 days. Option D is 17 days. I will stick with D being correct based on standard poultry science references for Japanese quail which is the commercial standard. Wait, some sources say 16 days. Let's check carefully. 'Quails have incubation period of' MCQs often appear in PPSC/FPSC exams. A quick mental search suggests 17-18 days is standard. I will keep D as correct but note that 16-18 is the range. Actually, many specific exam keys say 17 days. I'll maintain D.