To find a word's meaning, the reader can study the surrounding words, which are called the
antonym clues
context clues.
word parts
root words

Context clues

Explanation:

Context clues are hints that an author gives to help define a difficult or unusual word within a book. The clue may appear within the same sentence as the word to which it refers or it may follow in the next sentence. Because most of our vocabulary is gained through reading, it is important that we are able to recognize and take advantage of context clues.

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).

the answer is subjective. i personally agree with the first answer for this question.

if one isn't strictly talking about objects then the correct answer would be 'my eyes' since according to this riddle i am asleep and in order to answer/open the door i need to open my eyes first of all.

however, if one is specifically looking for an object, then the first thing i would open would be the door

hope this !