没多大区别，虽然后面一定是矛盾的，固然前后可以矛盾，也可以不矛盾。 比如： 虽然/固然 小明的成功很好，但是小红的更好。意在说明小明不好，小红的才好。这里是否定虽然和固然。 固然 小明的成功很好，小红的也不错。意在说明小红和小明都很好。 这里是肯定固然。 固然可以代替虽然，虽然不能代替固然。 另外，固然只用于口头语。

她（虽然　）很不高兴，但还是答应了。（虽然，固然） ？ 法国菜（ 固然　　）好吃，但意大利饭也很可口（虽然。固然）？ 她（虽然 ）不会为这样的事生气，但你这样做总有点儿不合适。（虽然，固然）？ 虽然( conjunctive in modern Chinese, but meaning 'even being so, although beig so' in ancient Chinese and only used as predicate, though) should be the answer to All the sentences you gave above. Acutually, 固然(adjective in moder Chinese, meaning 'in spite of something', but literally meaning 本来如此 'originally being so' in Ancient Chinese, used as predicate too) is Never used in any of the above senteces. 虽然 has changed into a pure conj. in Chinese, used with a sentence(possibly elliptical), both in the beginning and after the subjects. 固然 is an adv. in modern Chinese, used with a predicative phrase, and almost never used to start a sentence. This is the first difference between the two, when they function to mean the equivalent sense. 虽然=although. Sentences put together with 虽然...但是（/还是）convey opposite meanings respectively, while those jointed with 固然...也 have compatible meanings. And the second, and most important difference is that 虽然is a common word in both spoken and writing Chinese, while 固然is much formal/refined/literary, and this is the reason why in the third sentence 固然 other than 虽然 is suitable.

你写的三个填空题，我觉得1、3用”虽然“比较好。因为后面紧接的半句话表示了一个转折； 第二题用”固然“：法国菜（固然）好吃，但意大利饭也很可口。这里的”固然“的意思，表示法国菜本来就很好吃，这是很多人都接受的一个事实。而”意大利菜也很可口“，这与”法国菜好吃“不矛盾，所以不用”虽然“。 明白了？

“虽然”表示转折，一般与“但是“连用； “固然”也表转折的意思，但是多了一层意思,"本来就是这样"的意思。

她（虽然/固然　）很不高兴，但还是答应了。（虽然，固然） ？ 法国菜（　固然　）好吃，但意大利饭也很可口（虽然。固然）？ 她（虽然/固然 ) 不会为这样的事生气，但你这样做总有点儿不合适。（虽然，固然）？ 备注：虽然.......但是/可是/然而/却 固然.......但是/可是/却/也/就是