Final answer:
An ultrasound is the test used to indicate a fetus with conditions such as myelomeningocele or omphalocele, due to its safe application during pregnancy and ability to detect physical abnormalities.
Step-by-step explanation:
The test that would indicate a fetus with a myelomeningocele or omphalocele is c) Ultrasound. Ultrasounds are imaging studies that can be used safely during pregnancy and are routinely used to inspect the developing fetus for any anomalies. They can typically identify structural abnormalities like myelomeningocele, which is a type of spina bifida where the spinal cord and membranes protrude from an opening in the spine, and omphalocele, which is a birth defect where the infant's intestine or other abdominal organs are outside of the body because of a hole in the belly button area. Other tests such as amniocentesis can provide detailed genetic information, but the first indication of these conditions is usually detected via ultrasound.