单词拼写。（共6题，计6分）
Polluting the environment is a danger to the ______________ [sə'saɪəti]
He ____________ [dɪ'vaɪdɪd] his class into four groups to practice playing basketball.
He worked so hard that he without _________________ [daʊt] is the winner in the exam. .
___________ ['enəmɪz] can be turned into friends.
What does Lucy usually do in her ________________ [speə(r)] time?
He was __________ [nɒkt] down by a car yesterday.