Problem 1398 (difficulty: 5/10)

Which of the following is simply connected?

\(\displaystyle \R^2\setminus\{(0,0)\} \qquad \R^3\setminus\{(0,0,0)\} \qquad \R^3\setminus\{t,0,0): t\in\R\} \qquad \R^4\setminus\{t,0,0,0): t\in\R\} \)

Give me another random problem!