A client, a gravida 3 para 2 at 35 weeks’ gestation, comes in to the antepartum clinic for a check-up. She has been experiencing backaches after standing all day at her job as a grocery clerk. Which of the following exercise would the nurse suggest to relieve backache

A. The pelvic tilt.
B. Squatting.
C. Stretching.
D. Walkin

在我国的环境空气质量标准中，根据粉尘颗粒的大小，将其分为（）和（）。