Which of the following frequency planning methods must use the radio frequency hopping

A．That same day.

B．Friday of that week.

C．Saturday of that week.

D．Tuesday of the following week.

A.where

B.when

C.which

D.by which

A.in which

B.in that

C.at which

D.on which

【C18】

A．on that

B．on which

C．at that

D．at which

A.who is

B.who are

C.which are

D.which is

A.who

B.that

C.in which

D.of which

【C16】

A．in which

B．from which

C．of which

D．by which

Which of the following processes will increase salinity of ocean waters？

A．Evaporation.

B．Precipitation.

C．Melting.

D．Dilution.

A.that

B.which

C.what

D.by which

The work "Their" in line 20 refers to which of the following？

A．Elements

B．Monitors

C．Customs

D．Practice