15.a. Read the facts about sports equipment. Then, fill in the right form of the verb.
1. The tennis balls used at the Wimbledon Championships had been white since 1877. To make them more visible against the grass on television, they became yellow in 1986.
If it ... (not be) necessary to be more visible on TV, the tennis balls ... (not become) yellow.
2. The shoe market offers a broad range of products, from boots, sandals and high heels to sports shoes and technical footwear, Nike, Adidas and Under Armour are all dominating brands when it comes to sports shoes, but Nike is the champion, owning a 90% market share.
If Nike ... (not be) a champion brand, Adidas and Under Armour ... (be) the most famous ones.
3. A Spalding basketball is made of rubber and leather and its lifespan is 4-5 years, which means it bounces 10,000 times. The Spalding basketball ... (break) easily if it ... (not be made from a combination of leather and rubber. ​