¡no tarde!
a. lea b. llegue c. den

Correct b. llegue

First of all, this is a negative sentence. Negations using no is the most basic type of Spanish verb negation. To make a sentence negative, just place the word no before the conjugated verb. So the conjugated verb here is llegue that comes from the verb llegar and is its conjugation that matches the subject pronoun usted (formal you) in the imperative mood. Sentences in this mood are commands, so this sentence is a command. Finally:

¡No llegue usted tarde!

Doble a la derecha" means; "turn right" how does "siga derecho" mean "go (or follow) straight"

For this question, it will be important to use the words "mejor" (better), "lo mejor" (the best), and "lo peor" (the worst). while "mejor" is comparative (you are comparing one thing to something else), "lo mejor" and "lo peor" are superlative (there is nothing else better or worse than what these words are describing - there is no comparison).  you could say something like: la música rap es mejor que la música clásica - que es lo peor - pero la música rock es lo mejor de todas las formas de la música (rap music is better than classical music - which is the worst - but rock music is the best out of all the forms of music).