单项选择题
A.simpler than B.more difficult than C.not yet understood D.the same as
A.It is becoming more accurate. B.It is more accurate than the biological sciences. C.It is more accurate than some of the measurements of structural engineers. D.It is relatively inaccurate.
A.the skill of the scientist B.the extent to which variables can be controlled C.the requirements of the observer D.the development of more accurate instruments