之【zhī】
1. used between an attribute and the word it modifies 2. used in objective noun or pronoun
[助] 1、表示表示领有、连属、修饰关系 [代] 2、代替人或事物

健康才是真正的无价之宝。
Health is a jewel of great price.

做事情必须要有持之以恒的精神。
Perseverance is a necessity in work.
支【zhī】
1. prop up; put up; support 2. support 3. for long, thin things
[动]1、撑持,伸出,竖起 2、用物质或精神鼓励、帮助 [量]3、用于杆状的东西以及队伍、歌曲、乐曲等

他习惯用手支着头思考。
He has the habit of thinking with his head propped by hand.

看起来,他的确体力不支了。
It seems that he is worn out.

联欢会上,她唱了一支歌。
She sang a song in the party.
支撑【zhī chēng】
1. prop up; sustain; support 2. sustain; holdout; bear
[动]1、顶住物体使不倒塌 2、勉强维持

几根石柱支撑着那座小桥。
Several stone pillars support that small bridge.

由于生意清淡,这家店的营业收入只能支撑日常开销。
As the business is slack, the income of the shop can only sustain the daily expenditures.