Answer:
D. significance, which measures how likely it is
Explanation:
Statistical significance is a claim that a result is the outcome of any chance or random act but rather it is instead, likely to be the outcome of a specific cause. This claim is important especially for academicians and researchers for they rely heavily on the analysis of data.
The best way to connect the two given sentences is to use the words or phrase "significance, which measures how likely it is". The word "which" acts as the connector of the two sentences which have a related theme but also presents a different part of the objective.
Thus, the new sentence will read as-
In 2019, hundreds of scientists called for an end to reliance on statistical significance, which measures how likely it is that a result occurred by chance.