Which of the following is not a method of introducing alien $DNA$ into host cells?

Biolistics (gene gun) is suitable for:

During the process of gene amplification using $PCR$,if very high temperature is not maintained in the beginning,then which of the following steps of $PCR$ will be affected first?

Given below are two statements.
Statement $I$ - The isolated $DNA$ of donor organism is cleaved by suitable restriction endonuclease to form $DNA$ fragments with cohesive staggered or blunt ends.
Statement $II$ - The foreign $DNA$ or passenger $DNA$ can also be obtained directly from genomic or cDNA library.
In the light of above statements,select the correct option given below:

Which of the following is required for the amplification of a gene of interest by $PCR$?

Which method is used to amplify a desired gene in large numbers?