The beautiful park, _____ with thick trees, is much larger than what it used to be. [ ]

A. which surrounds

B. surrounded

C. surrounding

D. having surrounded

产生心电图机内部噪声的主要原因是（）。

A.环境噪音大

B.心电图机导联线接触不良

C.仪器周围有电磁噪声

D.心电图仪放大器元件损坏

E.放大器元件内部电子的不规则热运动