Men have weaker immune system
Sentence provides commentary information for elaboration of a concrete detail.
D) It was a good idea to wear short sleeves and a light jacket that could be taken off easily in the afternoon.
The concrete detail:
short sleeves and a light jacket
The commentary information for elaboration of the concrete detail:
that could be taken off easily in the afternoon.
Since you didn't provide the excerpt, I am going to assume that the answer you need is 'hearken'.

Because the ladder was in flat position not in slant.

Hello. You did not say which poem this question refers to, which makes it impossible for it to be answered accurately. However, I will try to help you in the best possible way.
In general, we can say that the first lines of a poem have the effect of determining the tone and the main subject which the poem will develop in the following lines. In this way, the first two lines can fulfill this role, mainly in relation to the tone of the poem.