The question below consists of a set of labelled sentences. Out of the four options given, select the most logical order of the sentences to form a coherent paragraph.
The causes and their
X-in the same series Y-one order, they stand Z-effects belong to the
Improve the bracketed part of the sentence. Scientists (have developed) an “organ-on-a-chip” platform to study how drugs are transported across the human placental barrier.