Automobiles certainly cause many problems ...

[Mori]

Which underlined word needs to be corrected?

Automobiles certainly cause many problems, however they fortunately provide us with benefits also.

Source: Jay Maurer, Focus on Grammar 5 third edition, page 361

I would change however to yet. I wonder what you think.

 

[Piscean]

I would change however to but.

 

[Tarheel]

Try:

Automobiles cause many problems, but they also provide us with benefits.

Do the advantages outweigh the disadvantages?

 

[Rover_KE]

@Mori, I have changed your thread title. As you know, titles must contain some or all of the word or words you are asking about.

 

[jutfrank]

It should be two sentences.

Automobiles certainly cause many problems. Fortunately, however, they also provide us with benefits.

 

[Tarheel]

There are many problems caused by automobiles. However, we can hardly do without them.

 

[Mori]

It should be two sentences.

Automobiles certainly cause many problems. Fortunately, however, they also provide us with benefits.

Thanks for the answer, but in that exercise, we're allowed to edit one underlined word only.

 

[emsr2d2]

Does the exercise instruct you to change just one of the underlined words and leave the rest of the sentence intact?

 

[Mori]

Does the exercise instruct you to change just one of the underlined words and leave the rest of the sentence intact?

Yes, exactly.

 

[Tarheel]

Thanks for the answer, but in that exercise, we're allowed to CHANGE one underlined word only.

 

[Tarheel]

@Mori When we are asked to edit something that word refers to the entire piece of writing -- not one word.

 

[emsr2d2]

Yes, exactly.

In that case, it's a very poor exercise. If I were to write that sentence from scratch, I'd probably keep "certainly" but I wouldn't use any of the other underlined words at all!
However, I assume they're not bothered about the naturalness of the sentence, only the grammar. If that's the case, then as Piscean said, "however" needs to be changed to "but". Its current position, directly after a comma, is incorrect.