(2014·安徽七校联考)It is difficult for children to change their eating habit later in life.________，parents should encourage healthy eating from an early age.

A．Otherwise　

B．Therefore

C．Besides　

D．However

当线岔处两支均为工作支时，在两接触线相距500mm外正线线岔的侧线接触线比正线接触线抬高的标准值为（）。

A、20mm

B、30mm

C、50mm

D、80mm