To estimate the expansion rate of the universe is a notoriously difficult problem because there is a lack of a single yardstick that all distances can be measured by.
Estimating the expansion rate of the universe is a notoriously difficult problem because there is no single yardstick by which all distances can be measured.
Because there is a lack of a single yardstick to measure all distances by, estimating the expansion rate of the universe is a notoriously difficult problem.
A notoriously difficult problem is to estimate the expansion rate of the universe because a single yardstick is lacking by which all distances can be measured.
It is a notoriously difficult problem to estimate the expansion rate of the universe because by no single yardstick can all distances be measured.
A选项：because之后跟着一个there be句型，其核心成分为“there is a lack”，即“这里有一个缺少”。但直接导致“估计速度是个难题的”应该是“没有标尺”这件事，而不仅仅是“这里有个缺少”。
另外一个题
The remarkable similarity of Thule artifacts throughout a vast region can, in part, be explained as a very rapid movement of people from one end of North America to the other.
The remarkable similarity of Thule artifacts throughout a vast region can, in part, be explained as
Thule artifacts being remarkably similar throughout a vast region, one explanation is
That Thule artifacts are remarkably similar throughout a vast region is, in part, explainable as
One explanation for the remarkable similarity of Thule artifacts throughout a vast region is that there was
Throughout a vast region Thule artifacts are remarkably similar, with one explanation for this being
正确选项D，中也包括there be句型，难道这不是光强调运动吗？（按照上一题的逻辑）应该强调的是人们从北美洲的一边到达另外一边。求大神