Final answer:
In the given sentences, 'while' and 'however' are used as signal words to indicate that a comparison is being made between the characteristics of carrots and beets.
Step-by-step explanation:
The words that signal two things are being compared in the sentences are 'while' and 'however'. These words are used to introduce a contrast between the characteristics of carrots and beets. When 'while' is used, it is indicating that there is a simultaneous difference in traits, showing how carrots being long and slender is in contrast to beets being red and round. 'However' serves as a transition to introduce the differing traits following a statement about similarities.