Questions

Controlled railroad crossing includes warning signs, red lights and railway gates, whereas absence of all of these warning signs like red lights and gates includes uncontrolled railroad crossings. 

To exit the PowerPoint application, you should Double click the application control menu icon or you can go to file menu and click exit button or you can close the window button.

Online marketing is the exchange of products and services between the buyers and sellers on the internet.It is also known as e-marketing or internet marketing or online advertising. It may take the form of : 

a.B2C where the products are sold directly to the customers. 

b.B2B where trading networks or auction sites maybe used to reach out to the new customers and serve the existing one

c.C2C where one customer may further sell the product to another customer.

Examples of online marketing may include banner ads, blogs, social network advertisement.

No circular or curved motion is possible without providing the necessary centripetal force. (C) provides this and so is the answer.