We think it most important that _______________(理论与实际相结合).

　　答案：theory be combined with practice

　　解析：be combined with...是固定搭配，意为"与......相结合"。Be connected with是指"将......连起来"，在含义上有所差别。其次，句首用了We think it most important that句型，暗示从句要用虚拟语气，should可以省略。