引起手足搐搦发作时，血清钙离子低于()。

A．1.0mmol/L

B．1.75mmol/L

C．1.88mmol/L

D．2.25mmol/L

E．2.75mmol/L

As a wise department manager, he possesses a unique way to ______ huge tasks into small and doable units.

A．break through

B．break away

C．break off

D．break down