下列调查中，适宜采用普查方式的是（　　）

饱和溶液____是浓溶液，如熟石灰的饱和溶液；不饱和溶液____ 是稀溶液，如接近饱和的硝酸钾溶液．（填“一定”、“不一定”）

公有制为主体、多种所有制经济共同发展是我国社会主义初级阶段的基本经济制度,其中对“公有制为主体”的正确理解是(   )

· Finding：Seniors, on average, bathe fewer than 3 times a week. And nearly 30% wash their hands only 4 times a day - half of the number doctors advise.

· Step：We touch our faces around 3,000 times a day - often inviting germs（病菌）to enter our mouth, nose, and eyes. Use toilet paper to avoid touching the door handle. And, most importantly, wash your hands often with hot running water and soap for 20 seconds.