There is generally agreement that feral swine are unwelcome – such as the Asian carp that are threatening to invade Lake Michigan, but that are far larger, more vicious and mounted on four legs.
A)such as the Asian carp that are threatening to invade Lake Michigan, but that are far larger, more vicious and mounted on four legs
B)like the Asian carp that have threatened an invasion of Lake Michigan, but far larger, more vicious, and mounted on four legs
C)like the Asian carp that are threatening to invade Lake Michigan, but are far larger, more vicious, and are mounted on four legs
D)like the Asian carp that are threatening to invade Lake Michigan, but far larger, more vicious, and mounted on four legs
E)such as the Asian carp that threaten to invade Lake Michigan, but are far larger and more vicious, and mounted on four legs
This topic has a lot of problems as far as parallelism and modification are concerned. Let's first take A.
A)such as the Asian carp that are threatening to invade Lake Michigan, but that are far larger, more vicious and mounted on four legs
It is not clear what the parallelism is around the conjunction 'but'. On the left of 'but' , you have - the Asian carp that are threatening to invade Lake Michigan - and on the right of 'but' you have -that are far larger, more vicious and mounted on four legs - missing the all important noun 'the feral swine' that are the larger and leg - mounted. It doesn't make a logical sense to say the carp are far larger than the swine and leg-mounted.
From B through E, the parallelism is not even structurally existent. On the left, you have a relative clause while on the right you have a list of three adjectives.
On modification, the larger, more vicious and the leg - mounted adjectives seem to modify the carp by virtue of their proximity rather than the swine that they are trying to describe.
In addition, it is not clear why the info about the carp is parenthesized while that info is essential to carry the intent of the sentence. If we remove the parenthesis within the dash and comma, the sentence does not seem to convey any meaning.
It is difficult to comprehend what this topic wants to teach.