In transabdominal scanning, a normal gestational sac can be consistently demonstrated when the beta hCG level is mega international units per milliliter (mIU/ml).

Explanation:

HCG (human chorionic gonadotropin) is the hormone produced during early pregnancy after implantation. Pregnancy kits are available to test the level of HCG in urine samples. In transabdominal scanning, beta HCG levels should be 1800 mIU/ml for a normal gestational sac. HCG level is very important to maintained to carry on the pregnancy. If it level drops it may leads to miscarriage.

So, the correct answer is 1800 mIU/ml.

poor water quality affects most estuarine organisms, including commercially important fish and shellfish. the pollutants that have the greatest impact on the health of estuaries include toxic substances like chemicals and heavy metals, nutrient pollution (or eutrophication), and pathogens such as bacteria or viruses.

the answer is b.) hydrogen bonds between bases.