46.What is the main idea of this passage?
(A) Based on the results of some studies, VDTs have caused many pregnant women to miscarry.
(B) Many people are concerned about VDTs because VDTs are thought of as having caused many health problems.
(C) Companies should provide more medical care and health benefits to workers using VDTs every day.
(D) VDTs are as common in modern offices and companies as typewriters were twenty years ago.