user: What are different types of grass?

assistant: There are more than 12,000 species of grass. The most common is Kentucky Bluegrass, because it grows quickly, easily, and is soft to the touch. Rygrass is shiny and bright green colored. Fescues are dark green and shiny. Bermuda grass is harder but can grow in drier soil.

user: How long did it take for ironworking to be commonplace in West Africa following its introduction in Northern Africa?

assistant: <think>
By the first millennium BCE, ironworking had been introduced in Northern Africa. Around that time it also became established in parts of sub-Saharan Africa, either through independent invention there or diffusion from the north and vanished under unknown circumstances around 500 CE, having lasted approximately 2,000 years, and by 500 BCE, metalworking began to become commonplace in West Africa. Ironworking was fully established by roughly 500 BCE in many areas of East and West Africa, although other regions didn't begin ironworking until the early centuries CE. Copper objects from Egypt, North Africa, Nubia, and Ethiopia dating from around 500 BCE have been excavated in West Africa, suggesting that Trans-Saharan trade networks had been established by this date.</think>
Ironworking was introduced in Northern Africa around the first millennium BCE and became commonplace in West Africa by 500 BCE. This means it took 500 years (1000-500) for ironworking to become common in West Africa following its introduction in Northern Africa.

user: From the passage list down the location of Visa data centers. List the results in semi colon separated format.

assistant: <think>
Visa Inc. (/ˈviːzə, ˈviːsə/; stylized as VISA) is an American multinational financial services corporation headquartered in San Francisco, California. It facilitates electronic funds transfers throughout the world, most commonly through Visa-branded credit cards, debit cards and prepaid cards. Visa is one of the world's most valuable companies.

Visa does not issue cards, extend credit or set rates and fees for consumers; rather, Visa provides financial institutions with Visa-branded payment products that they then use to offer credit, debit, prepaid and cash access programs to their customers. In 2015, the Nilson Report, a publication that tracks the credit card industry, found that Visa's global network (known as VisaNet) processed 100 billion transactions during 2014 with a total volume of US$6.8 trillion.

Visa was founded in 1958 by Bank of America (BofA) as the BankAmericard credit card program. In response to competitor Master Charge (now Mastercard), BofA began to license the BankAmericard program to other financial institutions in 1966. By 1970, BofA gave up direct control of the BankAmericard program, forming a cooperative with the other various BankAmericard issuer banks to take over its management. It was then renamed Visa in 1976.

Nearly all Visa transactions worldwide are processed through the company's directly operated VisaNet at one of four secure data centers, located in Ashburn, Virginia; Highlands Ranch, Colorado; London, England; and Singapore. These facilities are heavily secured against natural disasters, crime, and terrorism; can operate independently of each other and from external utilities if necessary; and can handle up to 30,000 simultaneous transactions and up to 100 billion computations every second.

Visa is the world's second-largest card payment organization (debit and credit cards combined), after being surpassed by China UnionPay in 2015, based on annual value of card payments transacted and number of issued cards. However, because UnionPay's size is based primarily on the size of its domestic market in China, Visa is still considered the dominant bankcard company in the rest of the world, where it commands a 50% market share of total card payments.</think>
Ashburn, Virginia; Highlands Ranch, Colorado; London, England; Singapore