I saw Mary dancing at the party and on such ______ she was really excellent. A. scenes B. situations C. positions D. occasions 答案:D在20以内的自然数中,既是质数又是偶数的数是(__________);既是质数又是奇数的数有(____________);既是奇数又是合数的数有(____________);既是偶数又是合数的数有(__________);既不是质数又不是合数的数是(__________)。