Of course, they must be careful not to let it take up too much of their time because study is still their primary responsibility.
当然，他们也必须小心，不要让打工占据太多时间，因为学业仍然是青少年首要的责任。
Of course, they must be careful not to let it take up too much of their time because study is still their primary responsibility.
当然，他们必须小心，不要让它占用太多的时间，因为学习仍然是他们的首要责任。
Old people must be very careful as they climb a staircase.
年长的人在上楼梯时，必须得小心。
Third, they must be very careful and cautious.
第三，他们必须非常小心和谨慎。
Third, they must be very careful and cautious.
第三，他们必须非常小心和谨慎。
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