请教以下这篇完型填空的答案?

请教以下这篇完型填空的答案?
Fear and its companion pain are two of the most useful things that men and animals possess,if they are properly used.If fire did not hurt when it burnt,children would play with it __11___their hands were burnt away,___12____,if pain existed but fear did not,a child would burn itself again and again,because fear would not __13___it to keep away from the fire that had burnt it before.Fear and pain are therefore two guards ___14___which men and animals might soon die out.
In the first sentence we suggest that fear ought to be properly used.If ,____15_______,you never go out of your house ___16_____of the danger of being knocked down and killed in the street by a car,you are letting fear rule you too ___17____.
Even in your house you are not absolutely ___18____:an airplane may crash on your house or you may get cancer!
The important thing is not to let fear rule you,but ____19______to use fear as your servant and guide.Fear will warn you of dangers; ____20____you have to decide what action to take.
11.[a]because [b]if [c]though [d]until
12.[a]Generally [b]Probably [c]Similarly [d]Consequently
13.[a]warn [b]request [c]manage [d]protect
14.[a]with [b]without [c]for [d]against
15.[a]after all [b]by chance [c]for example [d]in fact
16.[a]regardless [b]because [c]in terms [d]in front
17.[a]little [b]more [c]many [d]much
18.[a]firm [b]calm [c]safe [d]strong
19.[a]instead [b]better [c]similarly [d]further
20.[a]then [b]otherwise [c]likewise [d]even

11.[d]until
12.c]Similarly
13.[a]warn
14.[b]without
15.[c]for example
16.[b]because
17.[d]much
18.[c]safe
19.[c]similarly
20[c]likewise