My early_______ at learning playing the piano was a failure although I took a fancy to it.

A．attempt

B．effort

C．assumption

D．intention

为预防结石复发，下列需要酸化尿液的结石是

A．草酸结石

B．尿酸结石

C．黄嘌呤结石

D．氨基酸结石

E．磷酸盐结石