Incorrect

Incorrect	We realized where our weak points were and how to get rid of them.
Correct	We realized where our weak points were and how we could get rid of them.

Incorrect	All I know is my friend is right.
Correct	All I know is that my friend is right.
	Note : When the "that clause" is the object of a verb, the subordinating conjunction that may be omitted. When it is a complement of the verb be, that cannot be omitted.

Incorrect	Most of us found difficult to comprehend his speech.
Correct	Most of us found it difficult to comprehend his speech.

Incorrect	Her heart sank and could hardly stand.
Correct	Her heart sank and she could hardly stand.
	Note : Not changing the subject will make "her heart" seem to have "feet" on which it stands.

Incorrect	While doing the work, there are obstacles ahead.
Correct	While doing the work, they met with obstacles.
	Note : A certain action must be attached to the actor; otherwise the action becomes dangling.

Incorrect	Mandy is easy to suffer from cold.
Correct	Mandy suffers from cold easily.

Incorrect	How much is the price of this pen ?
Correct	How much is this pen ? Or How much does this pen cost ? Or What is the price of this pen ?