A tornado warning is issued
a. when weather conditions suggest that a tornado might form.
b. only when a tornado has been sighted.
c. only when a tornado has been indicated on radar.
d. when a tornado has been either sighted or indicated on radar.
Question 2
A chemical combination of two or more substances in variable proportions is called
a. a mixture.
b. a compound.
c. an ion.
d. a molecule.