# 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.

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.

A. 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.

B. 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.

C. 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.

D. 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.

E. It is a notoriously difficult problem to estimate the expansion rate of the universe because by no single yardstick can all distances be measured.

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