The Link Between Thalidomide Ingestion and Birth Defects

The link between thalidomide ingestion and birth defects

A) was easily traced because pregnant mothers had obvious violent reactions to the sedative.
B) was difficult to establish because many pregnant mothers had no obvious side effects or reactions to the sedative.
C) was obvious before the children were born but not able to be rectified.
D) had been established in previous research to have been harmful to animals.