No error.
Each is used in front of a Singular Noun followed by a Singular Verb.
The use of their (Plural Pronoun) is becoming or common these days.
Look at the examples given below :
Each student has been given his or her own email address.
Each student has been given their own email address.
Each of, each one of and everyone of followed by a Plural Noun/Pronoun take Singular Verb. as in –
Each of the houses is different.

Correct Option: D

No error.
Each is used in front of a Singular Noun followed by a Singular Verb.
The use of their (Plural Pronoun) is becoming or common these days.
Look at the examples given below :
Each student has been given his or her own email address.
Each student has been given their own email address.
Each of, each one of and everyone of followed by a Plural Noun/Pronoun take Singular Verb. as in –
Each of the houses is different.

had already begun will replace was already begun because –
Past Perfect Tense will be used here.
Past Perfect Tense is used for showing an action happened in the Past before another event took place.
Look at the example given below :
By the time I got home yesterday, my mother had already cooked dinner.
Hence, the show had already begun is the right usage.

Correct Option: C

had already begun will replace was already begun because –
Past Perfect Tense will be used here.
Past Perfect Tense is used for showing an action happened in the Past before another event took place.
Look at the example given below :
By the time I got home yesterday, my mother had already cooked dinner.
Hence, the show had already begun is the right usage.

eye will replace eyes.
eye – surgery is the right phrase that should be used.
We can also use ocular – surgery.
ocular : connected with the eyes.
Hence, for the delicate eye-surgery is the right usage.

Correct Option: C

eye will replace eyes.
eye – surgery is the right phrase that should be used.
We can also use ocular – surgery.
ocular : connected with the eyes.
Hence, for the delicate eye-surgery is the right usage.

between 1980 and 1990/from 1980 to 1990 will replace between 1980 to 1990 because –
between (Prep.) indicates a period of time that separates two days, years, events, etc.
between is used with and
from(Prep.) is used for showing when something starts from is used with to
to is never used with between
Look at the examples given below :
We shuttled between New York to Chicago. (×)
We shuttled between New York and Chicago. ( )
We are open from 8 a.m. to 7 p.m. every day

Correct Option: B

between 1980 and 1990/from 1980 to 1990 will replace between 1980 to 1990 because –
between (Prep.) indicates a period of time that separates two days, years, events, etc.
between is used with and
from(Prep.) is used for showing when something starts from is used with to
to is never used with between
Look at the examples given below :
We shuttled between New York to Chicago. (×)
We shuttled between New York and Chicago. ( )
We are open from 8 a.m. to 7 p.m. every day

capable of doing will replace capable to do because capable agrees with of (Prep.) and – ing Verb (Gerund).
Look at the examples given below :
I am perfectly capable of doing it myself.
The workers are capable of running the organisation them selves.
Hence, capable of doing this work is the right usage.

Correct Option: B

capable of doing will replace capable to do because capable agrees with of (Prep.) and – ing Verb (Gerund).
Look at the examples given below :
I am perfectly capable of doing it myself.
The workers are capable of running the organisation them selves.
Hence, capable of doing this work is the right usage.