Option 1 states that membrane lipids of chill-sensitive plants have a low proportion of saturated fatty acids. This means that the lipids would contain mostly unsaturated fatty acids. However, the correct answer states that the membrane lipids have a high proportion of unsaturated fatty acids. So, option 1 is incorrect.

Option 2 states that membrane lipids of chill-sensitive plants have a low proportion of unsaturated fatty acids. This contradicts the correct answer, which states that the lipids have a high proportion of unsaturated fatty acids. Therefore, option 2 is incorrect.

Option 3 states that membrane lipids of chill-sensitive plants have an equal proportion of saturated and unsaturated fatty acids. This contradicts the correct answer, which states that the lipids have a high proportion of unsaturated fatty acids. So, option 3 is incorrect.

Option 4 states that membrane lipids of chill-sensitive plants have a high proportion of unsaturated fatty acids. This aligns with the correct answer and provides an accurate explanation. Therefore, option 4 is correct.