Thewheelsofthefirstroadvehicleswerefashionedfromcrudestonedisks.
Batsfly,ratherthanglide,andthusaretheonlymammalscapableoftrueflight.
Withlasersscientistscanprobemanyphysicalprocesses,suchascombustion,oncebeyondourken.视野
InthenortheasternUnitedStates,itrainsintermittently间歇地throughoutthespring.
Communicationisoneofthemostimportantbondsthatholdculturalsystemstogether.