9月19日农业部验收专家组宣布：“杂交水稻之父”袁隆平院士最新培育的“Y两优2号”杂交水稻，亩产达到926.6千克．杂交水稻的培育是以下列哪项为基础（　　）

A．物种多样性

B．基因多样性

C．生态系统多样性

D．都不是

While a client with hypertension is being assessed, he says to the nurse, "I really don't know why I'm here. I feel fine and haven't had any symptoms. " Which of the following would be the nurse's best response

A．"Symptoms of hypertension are often not present. "

B．"Symptoms of hypertension signify a high risk of stroke. "

C．"Symptoms of hypertension occur only with malignant hypertension. "

D．"Symptoms of hypertension appear after irreversible kidney damage has occurred. "