潮间带满潮池中常见的滨螺是捕食者，吃很多藻类，尤其喜食小型绿藻(浒苔)。下图为藻类种数与滨螺密度的关系，下列说法错误的是

A．各种藻类存在竞争关系

B．若没有滨螺，藻类多样性会降低

C．滨螺密度越大，藻类种类数越少

D．滨螺在中等密度时，藻类多样性程度最高

In contrast to the new teachers, the middle-standing and veteran teachers seem to have made a remarkable improvement in their ability to ______.

A．be fair to any pupil

B．evaluate pupils' progress

C．present materials clearly

D．understand and play with pupils