安全认证是以安全标准为依据，对商品所进行的认证，只说明该产品符合安全指标，不评价其质量优劣（）
参考答案：对
--- I called Nina several times, but she didn't answer.
--- Of course, she ____________ London for a visit. [ ]
A. has been to
B. has gone to
C. has been in
D. had gone to
低压进线接户线对地面的距离，跨越通车街道时，不应小于（）。
A.4m
B.5m
C.6m
D.8m
