A signal indicating zone time is preceded with the letter（）.

A.a code hoist to indicate Greenwich mean time to follow
B.the letter G
C.the letters GT
D.the letter Z

A.darkening，growing in size and forming an anvil top
B.that shows extensive vertical development
C.creating cold downdrafts that are felt on the ground
D.All of the above

A.administer oxygen
B.immediately check his pulse and start CPR
C.make the victim comfortable in a bunk
D.immediately give a stimulant，by force if necessary