Final answer:
To and too are commonly confused words. 'To' is a preposition indicating direction or motion, while 'too' means 'also' or 'excessively'.
Step-by-step explanation:
To and too are commonly confused words. 'To' is a preposition indicating direction or motion, while 'too' means 'also' or 'excessively'. 'The journey was too tiring for us to enjoy' is an example of using 'too' and the to-infinitive. In sentence 2, it should be 'The girls were too happy to stop smiling.' In sentence 3, it should be 'The knife was too blunt for us to use.' In sentence 4, it should be 'He was too shocked to say a word.' In sentence 5, it should be 'The lady was too exhausted to climb the stairs.' In sentence 6, it should be 'The patient was too sick to speak.' In sentence 7, it should be 'The problem was too tricky for us to solve.' In sentence 8, it should be 'The program was too boring for us to want to watch it.'