The traffic rule says young children under the age of four and _____ less than 40 pounds must be in a child

safety seat. [ ]

A. being weighed

B. to weigh

C. weighed

D. weighing

自然组织谐波成像采用的基础技术是（）。

A.发射高频率超声波

B.窄带高通滤波技术

C.宽带低通滤波技术

D.多段电子聚焦技术

E.二维阵探头技术