The quality of EGC messages is（）affected by the position of the ship, the time of reception and climatic conditions.

A.sometimes

B.all times

C.never

D.partly

以下肿瘤常见于后纵隔的是

A．畸胎瘤

B．胸腺瘤

C．霍奇金淋巴瘤

D．神经节母细胞瘤

E．精原细胞瘤