People renewed their interest in natural gas as a fuel as a result of ______ of the late 1960s and early 1970s.

A．They strongly believe in family rules.
B．They are very likely to succeed in life.
C．They tend to take responsibility for themselves.
D．They are in the habit of obeying their parents.

A．The tickets have already been sold out.
B．They will probably not be able to get the ticket.
C．They have to wait for a long while to get the ticket.
D．They have to wait fifty minutes before they get the ticket.