Furious形容詞句首用法?

有些形容詞在當主詞補語用時，可以接介系詞，再接受詞的。如：
I am interested in English.
I am afraid of dog.
He was furious with her.

The hun leader was furious at what the emperor had done.非that的子句，可以做介系詞的受詞。
Being furious (at) that the emperor had escaped, the hun leader drew his sword.
但因為that子句不受介系詞的約束，所以此句中不可加at。
being ...是分詞構句，修飾主句的述部，屬副詞性質。提供原因。
= Because the hun leader was furious that the emperor had escaped, he drew his sword.

你給的例句可能不完整。前面缺了being...

1，還原本句The hun leader (who was furious that the emperor had escaped) drew his sword sword.   將形容詞Furious 提前於句首有強調用意形容主詞leader，而that所引導子句 the emperor had escaped當副詞修飾furious。
2，Expressive of the future hope of our country is the enthusiasm with which the new generation is engaged in affairs of state.取自網路，寫於一整句用法。. 這類句子，被置句首的主詞補語，其形式有形容詞，分詞，及介系詞片語等

The hunting leader-----S
(who is furioused)-----relative pronoun in defining clause;(=adj.;uncontrolled, full of fury)
or
in being=being=being furious with no @=no preposition=participial verbal adjective  qualifying nn "hun" but retaining some properties of a verb "furioused" =an adj./ adv.particle when "being" is retained.
that the emperor had escaped----adv cl to "is furioused"/"being furious"
drew his sword-------vt +Object---no need the subject (he) again
Or on rearrangement:-
Since he ----adv phrase with pp tense; a dependent cl
was furious----v--in coordinating
that the emperor had escaped---adv cl of concession ; pp
the hun drew his sword---main cl ----- S + vt