有关糖类物质概念的叙述中，正确的是

A．糖类都是具有甜味的物质

B．糖类都是符合通式Cn(H₂O)m的物质

C．葡萄糖具有还原性，它是一种多羟基醛

D．淀粉是一种白色粉末，本身有甜味

When experiencing heavy winds，you should reef sails to（）.

A.bring the sails parallel to the wind

B.reduce sail area exposed to the wind

C.allow the sails to catch more wind

D.remove all tension on the main and jib sheets