When to use "develop" in passive from? Here are two sentences from TEM-8 Exam (the most professional one in china) A:All social units develop a culture. Even in two-person relationships, a culture develops in time. The standard answer says we should use "is developed" instead of "develops". B: If you are continually surrounded by speakers of the language you are learning, you can ask them directly, but often this opportunity does not exist for the learner of English. So dictionaries have been developed to mend the gap. The standard answer says we should use "have developed" instead of "have been developed". It confuses me,even after looking up dictionary.