also will come after but because –
like either — or,neither — nor,not only — but also are the right Correlatives.
Look at the examples given below :
He is not only wise but also kind.
John plays not only drum but also flute.
not only — but also is used for emphasizing that something is also true.
Hence, but also on how you have written them is the right usage

Correct Option: C

also will come after but because –
like either — or,neither — nor,not only — but also are the right Correlatives.
Look at the examples given below :
He is not only wise but also kind.
John plays not only drum but also flute.
not only — but also is used for emphasizing that something is also true.
Hence, but also on how you have written them is the right usage

page after page will replace pages after pages because –
when words are repeated, they are always used in Singular.
Look at the example given below :

Correct Option: C

page after page will replace pages after pages because –
when words are repeated, they are always used in Singular.
Look at the example given below :

had left will replace left because –
when two actions happen in the past, it is necessary to show which action happened earlier than the other. The earlier action is expressed in Past Perfect tense and the later action in Simple Past.
Look at the examples given below :

Correct Option: C

had left will replace left because –
when two actions happen in the past, it is necessary to show which action happened earlier than the other. The earlier action is expressed in Past Perfect tense and the later action in Simple Past.
Look at the examples given below :

am will replace is because –
when the Subject of the Verb is a Relative Pronoun (who), the Verb (is) agrees in Number and Person with the Antecedent of the Rel. Pro.
A Noun/Pronoun which comes before a Rel. Pro. is called Antecedent.
Here, I is the Antecedent of who (Rel. Pro.) with I so, am is used.
Hence, who am to blame is the right usage.

Correct Option: B

am will replace is because –
when the Subject of the Verb is a Relative Pronoun (who), the Verb (is) agrees in Number and Person with the Antecedent of the Rel. Pro.
A Noun/Pronoun which comes before a Rel. Pro. is called Antecedent.
Here, I is the Antecedent of who (Rel. Pro.) with I so, am is used.
Hence, who am to blame is the right usage.

No error

Correct Option: D

No error
No error