I'd be glad to help you identify the errors in the sentences:
Sentence 1:
* Error: D
* Correction: "them" should be changed to "it" to maintain consistency with the singular pronoun "matter."
Sentence 2:
* Error: D
* Correction: "it" should be changed to "it" to refer back to "plan."
Sentence 3:
* Error: A
* Correction: "Little" should be changed to "Much" to correctly express the quantity of knowledge about the mysteries.
Sentence 4:
* Error: A
* Correction: "Almost" should be changed to "Most" to accurately indicate that the majority of voters are satisfied.
Sentence 5:
* Error: C
* Correction: "themselves" should be changed to "each other" to indicate that they are writing to each other, not to themselves.
Sentence 6:
* Error: D
* Correction: "on" should be removed as it is redundant. The phrase "the day when the country was completely liberated" already implies the specific day.
Sentence 7:
* Error: B
* Correction: "which are" should be changed to "which is" to agree with the singular subject "physics."