If Martin introduces an amendment to Evans’s bill, then Johnson and Ll

Very tough question. Not sure whether it is GMAT like question.

(A) if Evans speaks against Johnson’s position, Lloyd will not vote with Johnson.

The argument says if Martin introduces an amendment to Evans’s bill, then Johnson and Lloyd will both vote the same way. This implies that we can't say whether Johnson and Lloyd will both vote the same way if Martin doesn't introduce an amendment to Evans’s bill.
The argument again says Martin will introduce an amendment to Evans’s bill only if Evans speaks against Johnson’s position.
So, if Martin introduces an amendment to Evans’s bill, Evans MUST speaks against Johnson’s position. But this is NOT ALWAYS TRUE that if Evans speaks against Johnson’s position, Martin will introduce an amendment to Evans’s bill. So, we are not sure whether Martin will introduce an amendment to Evans’s bill. Hence, we are not certain whether Lloyd will or will not vote with Johnson. So, it may or may not be true.

(B) if Martin introduces an amendment to Evans’s bill, then Evans has spoken against Johnson’s position.

True. It is clearly paraphrased from argument.

(C) if Evans speaks against Johnson’s position, Martin will not introduce an amendment to Evans’ bill.

May be true.

Let's consider the following:

Y will happen only if X happens => If X happens Y may or may not happen.

The argument says Martin will introduce an amendment to Evans’s bill only if Evans speaks against Johnson’s position.
Y=Martin will introduce an amendment to Evans’s bill
X=Evans speaks against Johnson’s position

So, if Evans speaks against Johnson’s position, Martin may or may not introduce an amendment to Evans’ bill.

(D) if Martin introduces an amendment to Evans’s bill, then either Johnson will not vote with Lloyd or Evans did not speak against Johnson’s position.

There are two issues here,
a. If Martin introduces an amendment to Evans’s bill, then Johnson will not vote with Lloyd
The argument clearly says that if Martin introduces an amendment to Evans’s bill, then Johnson and Lloyd will both vote the same way. So, the above statement is NOT True.

b. If Martin introduces an amendment to Evans’s bill, then Evans did not speak against Johnson’s position
The statement says Martin will introduce an amendment to Evans’s bill only if Evans speaks against Johnson’s position. Therefore, it can not be happened that Martin introduces an amendment to Evans’s bill but Evans did not speak against Johnson’s position. So, it is NOT True.

(E) if either Evans did not speak against Lloyd’s position or Martin did not introduce an amendment to Evans’s bill, then either Johnson did not defend Lloyd or Martin spoke against Johnson’s position.

There are also two issues here,
a. If Evans did not speak against Lloyd’s position, then Johnson did not defend Lloyd.
The argument tells us that if Evans speaks against Lloyd’s position, Johnson will defend anyone voting with him. So, it can be true that if Evans did not speak against Lloyd’s position, then Johnson did not defend Lloyd.

b. If Martin did not introduce an amendment to Evans’s bill, then Martin spoke against Johnson’s position.
The argument says Martin will introduce an amendment to Evans’s bill only if Evans speaks against Johnson’s position. From this statement we are not certain if Martin did not introduce an amendment to Evans’s bill, whether Martin spoke against Johnson’s position. So it may be true.

D is the correct answer.

I dont think this is a GMAT question. More like a question which you have to just guess and move on, rather than breaking your head.