Asking for help

[frank]

Hello, everybody!
In reading a paper I encountered two  sentences:
(1) She is giving it deep thought.
(2) He gave no hint about his motives.
I know some sentences may also express the same meaning. For example,
(3) She is thinking about it deeply.
(4) He did not hint about his motives.
    Are there any shades of difference  in meaning between  pair (1) & (3) and pair  (2) & (4)?
  I'd quite appreciate it if anybody could explain it to me. 
Thank you!
With regards
Aipu Zhang

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