关于 We found it very difficult to learn a foreign language well 的句式的疑问

关于 We found it very difficult to learn a foreign language well 的句式的疑问
参考书上些的是We found it very difficult to learn a foreign language well.为什么不是 We found it was very difficult to learn a foreign language well.这样从句的主谓宾不都全了吗?