Question

TASK 4:Here are some

sentences from the
passage. Fill in the gaps with
prepositions from the box:
By for of in to The colour of the light (corresponding to the

energy of the photons) is determined by the energy required electrons .…………………. cross
the band gap of the semiconductor. White light

is obtained …………. Using multiple semi
conductors or a layer……………..light-emitting

phosphor on the semiconductor device.

Appearing as practical electronic components in

1962, the earliest LEDs emitted low- intensity infrared(IR) light. Infrared LEDs are used …………… remote-control circuits, such as
those used with a wide variety of consumer
electronics.​

Answer 1

Answer:

Sulfuric acid is sometimes referred to as the “king of chemicals” because it is produced worldwide in such large quantities. In fact, per capita use of sulfuric acid has been taken as one index of the technical development of a country. Annual production in the United States, which is the world’s leading producer, is well over 39 billion kg (86 billion pounds). It is the cheapest bulk acid.