选择可以替换划线部分的选项。— Aretheyyourparents? — No
题型：选择题
问题：
选择可以替换划线部分的选项。
— Are they your parents?
— No, they aren't. [ ]
A. isn't
B. are not
C. don't
D. do not
2. She is Ann. [ ]
A. She name
B. Her
C. She's name
D. Her name
3. How are your parents? [ ]
A. father and mother
B. father
C. mother
D. grandparents
4. His book is over there. [ ]
A. The boy's
B. The girl's
C. He
D. He's
5. These are my friends. [ ]
A. This
B. That
C. They
D. Those
=30°，γ=18kN/m3，墙背与填土间的摩擦角为δ。挡土墙重度γ=24kN/m3。挡土墙上底截面长度1m，土对挡土墙基底的摩擦系数为0.5。按照《建筑地基基础设计规范》(GB50007-2002)，回答下列问题：
平时，挡土墙的抗滑移稳定安全系数为（）。