___________Mrs Smith worked day and night, he found it difficult to make enough money to support such a large family.

A．Since

B．If

C．Once

D．Although

碎石桩法和砂桩挤密法加固砂性土地基的主要目的是：

A．提高地基土承载力

B．减少变形

C．增强抗液化性

D．渗漏问题