Poems of passage: booth, Collins, lorde

what is the "first lesson" described in the poem by this name?

a) how to float on one's back

b) how to do the backstroke

c) how to tread water when one is tired

d) how to identify the stars out at sea

It might be said that the first lesson of the poem is to float on one's back (option A) It seems that a father is teaching his daughter to swim on her back. This can be inferred by the use of certain words such as "Lie back daughter" "spread your arms wide". It also might be understood that the lesson is deep that that, It might suggest a father letting her daughter go, letting her be because she is going to be safe.