But he did not know why he had come to Philadelphia.

但他不知道他为什么来费城。

B.The reason why he did not tell others the truth was reliable.

为什么他没有告诉其他人事实的原因是可信的。（从句结构意思完整，用why在句中表明原因状语的作用，同时限定reason）

It is something far less pleasant, like being called in by his boss to explain why he did this, and why he did not do this or that .

这事可没那么爽心，可 能是上司传见，他解释他为什么这样做，为什么不那样弄或这样搞。

He had never told anyone of the dream, and he did not understand why he was telling Sam now, yet somehow it felt good to talk of it.

他从未对人说起过这个梦，更不明白自己此刻为何独对山姆敞开胸怀，但说出来的感觉真好。