dubious

他对针灸的益处持怀疑态度。

He's ___dubious about the benefits of acupuncture.

这一理论的证据充其量是值得怀疑的。

The evidence for this theory is ___dubious at best.

他在业内以名声可疑而闻名。

He is known in the industry for having a ___dubious reputation.