Question: how to make a newline with arrow in worksheet mode?

Hi, all, I have a confusion when I made a newline in worksheet mode. Usually, when I hit "shift+enter", then a newline is got. However, I found that in worksheet mode, when I hit "shift+enter", there is a newline, but there is no arrow appearing at the beginning of the newline while other worksheet file (not mine) has such a arrow at the beginning of each new line. any idea? my maple is maple12. thanks
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