The correct option is C that of other preying animals
In the given statement, a comparison is made between what puts koala bears in more danger, 'threat of bushes and pathogens' or 'threat of other preying animals'. The underlined phrase 'other preying animals' misses out on 'threat of', hence option D is incorrect. 'That' is demonstrative of 'threat of' and hence option B is correct. 'Those' in option A is incorrect because it refers to a plural noun and over here the noun 'threat' is a singular noun. Option C also misses out on 'threat' or the demonstrative of 'threat' and is an incorrect option.