Heres a detailed anwser!
A: Obesity
Yes, this is correct, an inactive lifestyle could make a person more likely to have obesity.
B: Weight loss
This is incorrect as in the question it states "inactive lifestyle" meaning the person is not doing anything. You will not loose weight from this. You will gain weight.
C. Sexually transmitted disease
No. By being inactive you will not get a sexually transmitted disease as this only happens when two people do it. Inactive lifestyle will cause weight loss. Not a disease.
D. Improved Sleep
No, you will not get improved sleep. When inactive, you may become sleepy, yes. But you will not get improved sleep since your body is not active.
Hope this helped <3