This is the most beautiful park I have _____ visited.

________ knowledge can be acquired from books，skills must be learned through practice.[ ]

Mary was much kinder to Jack than she was to the others, , of course, made all the others upset.

My son is old enough to ___ himself. He likes ___ blue, but this morning he __ his white T-shirt when he got up.

the wave of worldwide economic crisis,lots of people are out of work,joining the ranks of unemployed.