Here are the revised sentences using the phrases "in order to" and "so as to" as specified:

1) I spoke loudly in order to ensure that everybody could hear me clearly.

2) Mary often goes home as soon as the class is over so as to avoid making her mother wait for her.

3) These girls were talking in whispers in order to prevent anyone from hearing their conversation.

4) I spoke loudly so as to make sure that everybody could hear me clearly.

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