题目内容：

During a research experiment, a biologist placed a shark into a large tank and then ______ several small fish into the tank. As you would ______, the shark quickly swam around the tank, attacked and ate the smaller fish.

The biologist then ______ a strong piece of clear glass into the tank, creating two ______ tanks. She then put the shark on one side of the glass and a new set of fish on the other.______, the shark quickly attacked. This time, however, the shark ______ because it knocked hard against the glass.______, the shark kept repeating this behavior every few minutes, but ______. Meanwhile, the fish swam around ______ in the other part. Eventually, about an hour into the experiment, the shark ______. This experiment was carried out several times. Each time, the shark got less ______ and made fewer attempts to attack the fish, until eventually the shark got ______ hitting the glass divider and simply stopped attacking. The biologist then ______ the fiberglass divider, but the shark didn’t attack. The shark was trained to believe a/an ______ existed between it and the smaller fish, even when the fish swam ______ they wished, free from harm.

Many of us, after ______ setbacks and failures, readily give up and stop trying. Like the shark in the story, we believe that ______ we were unsuccessful in the past, we will always be unsuccessful.______, we continue to see a barrier in our heads, even when no 4 real, barrier exists ______ where we are and where we want to go, we ______ see obstacles in our heads.

1.A. recognized    B. refreshed    C. reflected    D. released

2.A. demand    B. expect    C. believe    D. require

3.A. identified    B. provided    C. inserted    D. transported

4.A. separate    B. opposite    C. relevant    D. connected

5.A. Meanwhile    B. Yet    C. Instead    D. Again

6.A. fainted    B. sank    C. bounced    D. rushed

7.A. Excited    B. Frustrated    C. Determined    D. Satisfied

8.A. in order    B. in vain    C. in pain    D. in secret

9.A. undefeated    B. unchallenged    C. unnoticed    D. unharmed

10.A. gave up    B. broke away    C. knocked off    D. let out

11.A. aggressive    B. calm    C. accurate    D. curious

12.A. sure about    B. involved in    C. tired of    D. familiar with

13.A. replayed    B. replaced    C. rebuilt    D. removed

14.A. distance    B. barrier    C. gap    D. edge

15.A. whatever    B. wherever    C. however    D. whenever

16.A. overcoming    B. observing    C. experiencing    D. forgetting

17.A. though    B. unless    C. while    D. if

18.A. In addition    B. In other words    C. As a result    D. Above all

19.A. between    B. among    C. with    D. around

20.A. suddenly    B. constantly    C. finally    D. carefully