在病因研究的轮状模型中，强调宿主与下列哪种因素的关系

A．生物因素

B．环境因素

C．物理因素

D．精神因素

E．化学因素

Concerning the identification signal for a pilot vessel，in fog，which statement is TRUE?（）

A.When at anchor，the pilot vessel is only required to sound anchor signals

B.The identification signal must be sounded any time the pilot vessel is underway

C.The pilot vessel may only sound the identity signal when making way

D.All of the above