Explanation

Scratch my back and I'll scratch yours means If you do me a favor, I'll return it."

Explanation

Many eukaryotes are unicellular organisms that, like bacteria,

They consist of only single cells capable of self-replication. 

Plasmids and bacteriophages can replicate within bacterial cells independent of the control of chromosomal DNA.

Explanation

Moin Akhter was a Pakistani television, film, and stage funny actor. 

He started as a comedian in 1966

His acting career as child actor at the age of 13

He made his television debut on 6 September 1966

Born: December 24, 1950, Karachi

Died: April 22, 2011 (age 60 years), Karachi

Years active 1966–2011

Awards:

• Pride of Performance (1996)
• Sitara-e-Imtiaz (2011)

Explanation

We are given:

x+y=10

xy=20

The sum of the reciprocals of the two numbers is: 1/x+1/y =x+y/xy

Substitute the given values:

=10/20

=1/2

Explanation

An adverb of frequency is used to indicate how often something happens (e.g., always, often, rarely, never).

It answers the question "How often?"

Explanation

In most sports, the referee signs the final result after the game to confirm the official score or outcome.

Explanation

Diffusion refers to the process by which molecules intermingle as a result of their kinetic energy of random motion.

It is the net movement of molecules or atoms from a region of high concentration to a region of low concentration.

This is also referred to as the movement of a substance down a concentration gradient.

Explanation

The correct punctuation is "History, it has been said, is the essence of innumerable biographies."

Commas are needed to set off the clause "it has been said."

Explanation

 Trojan Horse is malware that is installed on a computer without the user's knowledge and often runs malicious code.

Explanation

In passive voice, "She will have sung a song" becomes "A song will have been sung by her."

Passive voice changes the focus from the subject to the object.