Correct

还 vs 仍 vs 仍然

/ hái vs réng vs réngrán /
Strokes

Definition

还, 仍 and 仍然 are all Adverbs, which means “still; yet”.

Example

仍 and 仍然 are more literary and indicate that some state remains unchanged or resumes their original form.
In the four examples above, 还 can be used instead but is more colloquial.
1
réng
  
(
réngrán
仍然
  
)
shì
me
那么
jìng
  
,
hǎoxiàng
好像
shénme
什么
shì
méiyǒu
没有
shēng
发生
  

The night is still as before, as if there is nothing happening.

2
企业
zǒu
chū
kùnjìng
困境
  
,
réng
  
(
réngrán
仍然
  
)
yào
需要
dìng
一定
shíjiān
时间
  

It will still take some time for the enterprise to step out of its difficult position.

3
毕业
hòu
réng
  
(
réngrán
仍然
  
)
zài
yuánlái
原来
de
xué
大学
gōngzuò
工作
  

He returned to his original university to work after his graduation.

4
Kàn
zhèxiē
这些
liào
资料
hòu
  
,
qǐng
réng
  
(
réngrán
仍然
  
)
fàng
huí
yuánchù
原处
  

After reviewing the information, please still put it back.

还 is only used, to indicate comparison, supplement, etc., while 仍 and 仍然 can not be used like this.
For more 还 usage, please refer to 更 vs 更加 vs 还: https://www.cchatty.com/grammar/127955
5
Zhège
这个
rén
女人
nánrén
男人
hái
néng
gàn
  

The woman is more capable than a man.

6
Tàiyáng
太阳系
zhōng
chúle
除了
yǒu
qiú
地球
  
,
háiyǒu
还有
yuèqiú
月球
děng
xíngxīng
行星
  

In addition to the Earth, there are planets such as the Moon in the solar system.