Which element of syntax appears in both poems?
a. caesura
b. anaphora
c. meter
d. enjambment
e. paralell structure

The following element of syntax appear in both poems:

D. Enjambment.

Both poems present enjambment, as one can see on the first quatrain of "Imagery" or the verse that begins with "But to me..." in the case of "Summer Rain".

That said, one can argue that other elements are present on both poems.

In both poems, there are paralell structures. In "Summer Rain", on the lines that include verbs in the past tense ("rattled and clashed"; "danced and glittered") and in "Imagery", MacLeish uses it on "bosomed" and "blossomed".

One could argue as well the presence of anaphora, with the different repetitions on both poems. In "Summer Rain", the three "And"s, while "Imagery" has "All".

In any case, these other elements appear in a limited manner, so the answer is still D as enjambment is the primary element that is shared between poems.

.

explanation:

because they .

the following key ideas correctly express the key sentence.

restate key idea: most people can learn to swim in ten short lessons.

restate key idea: the majority of water-accident victims require mouth-to-mouth breathing.

restate key idea: an empty, tightly closed gallon jug will support a tired swimmer.  

restate key idea: first aid is to prevent accidents as well as assist in rescue.

explanation: the key idea needs to have the same topic as the key sentence (drowning and safety).