was will replace are because– when a Plural Noun is placed with a real Singular Subject (one, each, etc.) with of, the Verb will be Singular. Look at the examples given below : One of the boys is ill. Each of the girls is clever. Hence, was shot dead is the right usage.

contains will replace contain because – The fifth and final act (Main Subject) is in Singular. Hence, the Verb will also be in Singular as a Verb agrees with its Subject in Number. Singular Subject ® Singular Verb (Main Verb + S) Plural Subject ® Plural Verb (Main Verb without S) Look at the example given below: The great poet and scholar is dead. Here, scholar and poet refer to the same man. So, the Subject is in Singular and the Verb is also in Singular.

to enter will replace entering because – The to-Infinitive (Main Verb) : functions as a Noun, as Adjective, or an Adverb. In this sentence, permitted to enter, to enter is the direct object, the Noun that receives the action of the Verb (Permitted). To enter refers to a thing being done, or, desired to be done Hence, to enter the park is the right usage.

away will not be used because– to pass away (Phr. V.) : to die; end to pass time : to spend time, especially when you are bored or waiting for something/someone to pass (Verb) means to move past Look at the examples given below : The road was so narrow that cars were unable to pass. They passed the time until dinner talking and playing cards. My aunt passed away last month. The years of famine passed away and were followed by years of prosperity. Hence, to pass the time is the right usage.

had I will replace I had because – When a negative Adverb/Adverbial Expression (no sooner, hardly/barely/scarcely), is used at the beginning of a clause; it is followed by Aux. Verb + Subject.

Look at the examples given below :

No sooner had he finished dinner

                   ↓    ↓

            Aux.V. Subject

than he started feeling sick.

Hardly had she arrived, when problems started.

              ↓    ↓

        Aux. V. Subject

Hence, had I spoken is the right usage

There are no error

Subject   +                         Aux. Verb     +     Main Verb    +   by + ---

↓                                             ↓                            ↓                         ↓

Many accidents                 (be)  are                 caused                    by--------

                                                                                 ↓

                                                                  (Past Participle)

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.

by will replace with because – by (Prep.) is used for indicating the agent/object after a Passive Verb Agent/Object → his friend Passive Verb → accompanied With (Prep.) indicates being in the company of Look at the examples given below : His friend stayed with him in the hospital. He was knocked down by a bus. Hence, by his friend is the right usage.