Which is the best sentence out of the given words ? Is the use of 'and so' advisable?

Question

My friend and I are struggling with this question from our English textbook:

Choose the best sentence that can be made from the words given:
we / dependent / nature / cannot survive ourselves / without wildlife
a. As we are dependent on nature and we cannot survive ourselves without wildlife.
b. We dependent on nature and therefore cannot survive ourselves without wildlife.
c. We are dependent on nature and so cannot survive ourselves without wildlife.
d. We are dependent on nature and cannot survive ourselves without wildlife.

We can clearly see grammatical mistakes in a. and b., but we are not sure if both c. and d. are correct. Or is the textbook wrong?

Answer 1

To my (American) ear, the difference between c and d (which are both grammatically correct sentences, with a small caveat about "ourselves" vs "by ourselves") is that and so explicitly marks the second clause as a logical consequence of the first clause. Restating d to be more explicit might give you:

We are dependent on nature and [also] cannot survive by ourselves without wildlife.

Being more explicit about c would give you:

We are dependent on nature and [because of this] cannot survive by ourselves without wildlife.

Depending on what you are trying to say, either c or d could be correct.

Answer 2

IMO, the text book has made a slight mistake with the words.

'cannot survive ourselves' is not grammatically correct. It should be:

cannot survive by ourselves

If that was correct, the best sentences that can be formed using the words given in the text book would be :

We are dependent on nature and cannot survive by ourselves, without wildlife.

or

We are dependent on nature and thus cannot survive by ourselves, without wildlife.

Although, the use of 'without wildlife' is redundant, as it is clearly given that we cannot survive by ourselves. I've used it (and so should you) because it is given in book and you have been asked to use all the words.

Your option c. is not incorrect, but I've made a few changes.

We are dependent on nature and so we cannot survive by ourselves, without wildlife.