Which of the following are correct for Fluoroscopy?

Select one or more:

a)The technique is based on differential penetration of X-rays into different tissues.

b)Blood vessels can be highlighted without the need of a contrast medium.

c)Requires subtraction techniques to produce a clear image of blood vessels.

d)It does not allow constant imaging of blood vessels as interventional techniques are performed.

e)It is an invasive technique.

a andc is that correct please help