7.
下列是四种烷烃分子的球棍模型或结构简式,下列说法正确的是( )
\(\rm{①}\)
\(\rm{②CH}\)\(\rm{{\,\!}_{3}}\)\(\rm{CH}\)\(\rm{{\,\!}_{2}}\)\(\rm{CH}\)\(\rm{{\,\!}_{2}}\)\(\rm{CH}\)\(\rm{{\,\!}_{2}}\)\(\rm{CH}\)\(\rm{{\,\!}_{2}}\)\(\rm{CH}\)\(\rm{{\,\!}_{3}}\) \(\rm{③CH}\)\(\rm{{\,\!}_{3}}\)\(\rm{CH}\)\(\rm{{\,\!}_{2}}\)\(\rm{CH}\)\(\rm{{\,\!}_{2}}\)\(\rm{CH}\)\(\rm{{\,\!}_{2}}\)\(\rm{CH}\)\(\rm{{\,\!}_{3}}\)\(\rm{④CH}\)\(\rm{{\,\!}_{3}}\)\(\rm{CH}\)\(\rm{{\,\!}_{2}}\)\(\rm{CH}\)\(\rm{{\,\!}_{3}}\)