You should be careful________ driving. There are so many people on the street.
All the choices are prepositions.
I do not care for any of those choices.
I would use the conjunctions "when or while".
when - at what time? over what period?... this is used to refer to a specific time, e.g., When were you born? / When was the war of 1812? / I will tell you the secret when I see you.
while - at the same time that something else is happening / during or in the time that something elese is happening, e.g., He drowned while swimming / I will talk to you while I cook dinner.
So, I would write the sentence as follows: "You should be careful while* driving.
* during the time / for the period of time that you are driving.
As for slecting one of the options, I guess I would choose D - about, but I would never say it that way.
I agree entirely.
'When' or 'while' would be the most natural choices, but neither of these words is offered. Of those that are suggested, most options are possible, but none is quite right. As Paul says, 'about' is 'the best of a bad lot'. It is slightly more natural than the others, but not ideal.
It's a badly written question. Forget about it.
Thanks for all of you above. So what's the difference between these phrases？
Can I say?
①be careful of=watch out for. For example, be careful of the dog, or it will bite you.
②be careful with=deal sth. with care/carefullly. For example, be careful with your dog and take care of it gently.
③"be careful in"share the same usage with "be careful with", but usually ends with v-ing?
④be careful about=pay attention to sth. that you do. For example，be careful about what your eat if you want to be more healthy.
Is my analysis right？
I too think that none of these options work. 'About' is the best of a bad lot. 'When' or 'while' would both be fine options but neither are listed.
The best form would be : ' You should be careful <em>when</em> driving', but this is not in your list of options. D [<em>about</em>] seems the most suitable from the choices you have.
You can say 'You should be careful <em>in doing something'</em>, but it doesn't seem right in this case with 'driving'.