34. A. when             B. which         C. that              D. where

33. A. no               B. less          C. some              D. more

32. A. the researchers                   B. the experiment

C. the clock                         D. the brain

31. A. familiar with    B. focus on      C. make out          D. tell apart

30. A. partly           B. quickly       C. how               D. first

29. A. where            B. when          C. while             D. as

28. A. produced         B. carried out   C. tried             D. did

27. A. which            B. we            C. this              D. what

26. A. sleepy           B. bored         C. excited           D. active

25. A. change           B. develop       C. grow              D. slow