If it is always expressed it is dominant, also dominant allele is a possible answer. If it is not expressed unless both alleles are the same, it is recessive.
I think the answer is A. not entirely sure
The mass is increased as two things are added together so the two masses of the two substances are added together.
The disease is mainly caused by a lack of a slippery substance in the lungs called surfactant. This substance helps the lungs fill with air and keeps the air sacs from deflating. Surfactant is present when the lungs are fully developed.
https://medlineplus.gov/ency/article/001563.htm
