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.

with will replace on because
angry (Adj.) : feeling or showing anger (usually followed by at, with, or about (Prep.)
Look at the examples given below :
The girl felt angry at the injustice of the situation.
I was angry with myself for making silly mistakes.
We use angry at/about (something) and angry with (somebody).
Hence, is angry with the clerk is the right usage

Correct Option: B

with will replace on because
angry (Adj.) : feeling or showing anger (usually followed by at, with, or about (Prep.)
Look at the examples given below :
The girl felt angry at the injustice of the situation.
I was angry with myself for making silly mistakes.
We use angry at/about (something) and angry with (somebody).
Hence, is angry with the clerk is the right usage

are will be used after accidents because –
The sentence is in Passive Voice. The basic structure of a Passive clause is as follows :
It is also a general statement, hence, the Aux. Verb will be used in Simple Present Tense.
Hence, many accidents are caused by reckless driving is the right usage

Correct Option: C

are will be used after accidents because –
The sentence is in Passive Voice. The basic structure of a Passive clause is as follows :
It is also a general statement, hence, the Aux. Verb will be used in Simple Present Tense.
Hence, many accidents are caused by reckless driving is the right usage

read will replace has read -because the action took place in the past.
Hence, He read four plays is the right usage.

Correct Option: A

read will replace has read -because the action took place in the past.
Hence, He read four plays is the right usage.