A young boy sits outside in a grassy field with his back turned towards the viewer- he is holding a wooden toy that can be spun between your hands and launched into the air.
A young boy stands at the chalkboard to answer a math problem.
A boy can't sits and stands at the same time. You can only be doing one at a time.
If the young boy sits outside he can't stand at the chalkboard
A boy cannot sit and stand at the same time. One is unlikely to find a chalkboard in a grassy field. A child holding a wooden toy is likely engaged in play and not busy answering a math problem.