It hink French grammar is much (difficult) __________ to learn than Englishgrammar.

more difficult

【译文】我觉得法语语法比英语语法要难学得多。

【考点】形容词比较级

【解析】解题的关键是句子中的than。difficult是一个多音节词，其比较级和最高级是在前面加more和themost.