Although Aqueous Fluid Control Materials Are the Most Commonly Used

Although aqueous fluid control materials are the most commonly used commercial controls for blood gas and pH measurements,what is their main disadvantage?

A) They are dissimilar to blood by having lower viscosity and surface tension.
B) They must be shaken vigorously before being opened.
C) The buffer that is used contains high levels of lead.
D) They overestimate pH because the buffer is a weak base.