Question

Present perfect

Have / has +

past participle of verb

Uses:

a. Actions started in the

past and continuing

in the present

b. Unfinished period

of time

c. Unspecified period

of time

d. Experiences.

Gasoline has been

essential to our

transportation.

Many diseases have not

been eradicated yet.

Have vaccinations

impacted human health?

Past perfect

Had + past participle

Uses:

a. Actions finished before

other actions in past

Before the invention of

vaccines, smallpox had

killed millions of people.

Scientists thought

previous cultures had not

immunized themselves

against illnesses.

Had ancient cultures

eaten meat before they

discovered fire?

G

Answer 1

Respuesta:

que podemos aser por ti

Explicación: