1、I made up my mind and got started with my work.
我下定决心，开始工作。
2、They gave me a week to make up my mind.
他们允许我有一周的时间作决定。
3、I have many facts to chew upon before I make up my mind.
我在作出决定之前有许多情况要加以考虑。
4、I am old enough to make up my own mind.
我已经长大了，可以自己拿主意了。
5、I can't make up my mind whether to come or not.
我不能决定是去呢？还不去呢？
I can't make up my mind.
我下不了决心。
Time presses , make up your mind.
时间紧迫，速下决心。
He refuses to make up his mind.
他拒绝做出决定。
详细解释：
下定决心做某事，相当于be determined to do sth
特别要注意的一点就是：mind在这边是可数名词，make up their minds，make up my mind；
还有一个就是要注意和另一个词组的区别change one's mind改变某人的主意
mind在这边是不可数名词，change my mind，change their mind。