The number of women dying from breast cancer has fallen to its lowest level ____ records began in 1971.

1. A.
   when
2. B.
   before
3. C.
   since
4. D.
   after

The number of women dying from breast cancer has fallen to its lowest level ____ records began in 1971.

A．when          B．before       C．since        D．a(chǎn)fter

The number of women dying from breast cancer has fallen to its lowest level ____ records began in 1971.

A．when                     B．before            C．since             D．a(chǎn)fter

The number of women dying from breast cancer has fallen to its lowest level ____ records began in 1971.