男孩，2岁，因腹部隆起就诊，饮食、大小便等一般情况良好，无明显不适症状，无血尿。查体：右腹可及一肿物，大小5cm×6cm×6cm。

应采取的最佳治疗方案为（）

A.肾盂成形术

B.肾造瘘术

C.右肾切除术

D.保守观察

E.膀胱镜下输尿管双J管置入术

Once the durations of the activities are calculated for a completed network, a forward pass and a backward pass will provide ______.

A) the float of the activities
B) the early start and late start only
C) the critical path
D) A and C