Explanation:

All statements are correct.

• An ‘Application Programming Interface’ (API) is an interface that can be used to program software that interacts with an existing application.
• An open source API, also called public API, is an application programming interface made publicly available to software developers.
• Open APIs are published on the internet and shared freely, allowing the owner of a network-accessible service to give universal access to consumers.

APIs vs Web Services

• APIs and web services are not mutually exclusive. In fact, one is a subset of the other: every web service is an API — since it exposes an application’s data and/or functionality — but not every API is a web service.
• APIs are protocol agnostic. While APIs can use any protocols or design styles, web services usually use specific protocols. 

?What role does API play in trading?

• APIs have become increasingly popular with the rise of automated trading systems. In the past, retail traders were forced to screen for opportunities in one application and separately place trades with their broker. 
• Many retail brokers now provide APIs that enable traders to directly connect their screening software with the brokerage account to share real-time prices and place orders.

Hence option 4th is correct.