TOEFL Structure and Written Expression 12 (Longman PBT)

Different hormones __ at the same time on a particular target issue.

• usually act

• usually acting

• they usual act

• the usual action

The tidal forces on the Earth due to __ only 0.46 of those due to the Moon.

• the Sun is

• the Sun they are

• the Sun it is

• the Sun are

Most radioactive elements occur in igneous and metamorphic __ fossils occur in sedimentary rocks.

• rocks, nearly all

• rocks, but nearly all

• rocks, nearly all are

• rocks, which nearly all are

__ radioisotope is encountered, the first step in its identification is the determination of its half-life.

• An unknown

• Afterwards, an unknown

• When an unknown

• During an unknown

The Missouri __ longest river in the United States, flows through seven states from its source in Montana to its confluence with the Mississippi.

• River, the

• River is the

• River is one of the

• River, one of the

Coral islands such as the Maldives are the tips of reefs built during periods of warm climate, when __ higher.

• were sea levels

• sea had levels

• having sea levels

• sea levels were

Hail forms within large, dense cumulonimbus __ develop on hot, humid summer days.

• clouds

• clouds that

• clouds that are

• clouds that they

Measles is a highly contagious viral disease __ by a characteristic skin rash.

• accompany

• is accompanied

• accompanied

• it is accompanied

Charles Darwin's first scientific book, published in 1842, __ a since substantiated theory on the origin of coral reefs and atolls.

• to present

• presented

• presenting

• it presents

Phytoplanktons thrive where __ phosphorus into the upper layers of a body of water.

• upwelling currents circulate

• the circulation of upwelling currents

• are upwelling currents

• circulates upwelling currents