a) Open the brackets using verbs in the correct forms:
1 When the sellers quote prices they usually (to state) on what terms they (to deliver) the goods.
2 They also state at what prices the goods (to deliver).
3 If the goods (to offer) on fob terms the price will cover the cost of the goods and transportation expenses to the port of shipment.
4 If the goods (to offer) on cif terms the price (to include) cost, insurance and freight.
5 In case of fob terms the goods usually (to ship) on board ships or planes.
6 Terms of delivery can (to state) in different ways.

a) Open the brackets using verbs in the correct forms:
1 When the sellers quote prices they usually state on what terms they will deliver the goods.

Explanation: The subject "sellers" is followed by the verb "quote," which is used in the present tense. The pronoun "they" refers to the sellers, so the verb "state" should also be in the present tense. The phrase "on what terms" acts as an adverbial phrase and does not affect the verb tense. Finally, "will" is used to indicate future delivery.

2 They also state at what prices the goods will be delivered.

Explanation: The subject "they" refers to the sellers, so the verb "state" should be in the present tense. The phrase "at what prices" acts as an adverbial phrase and does not affect the verb tense. "Will be" is used to indicate future delivery.

3 If the goods are offered on fob terms, the price will cover the cost of the goods and transportation expenses to the port of shipment.

Explanation: The subject "goods" is followed by the verb "are offered," which is used in the present tense passive voice. The phrase "on fob terms" is an adverbial phrase and does not affect the verb tense. "Will cover" is used to indicate future coverage.

4 If the goods are offered on cif terms, the price includes cost, insurance, and freight.

Explanation: The subject "goods" is followed by the verb "are offered," which is used in the present tense passive voice. The phrase "on cif terms" is an adverbial phrase and does not affect the verb tense. "Includes" is used to indicate the present inclusion of cost, insurance, and freight.

5 In case of fob terms, the goods are usually shipped on board ships or planes.

Explanation: The subject "goods" is followed by the verb "are usually shipped," which is used in the present tense passive voice. The phrase "in case of fob terms" is an adverbial phrase and does not affect the verb tense.

6 Terms of delivery can be stated in different ways.

Explanation: The subject "terms of delivery" is followed by the verb "can be stated," which is used in the present tense passive voice. The phrase "in different ways" is an adverbial phrase and does not affect the verb tense.

Overall, these sentences describe how sellers quote prices and state the terms and conditions of the delivery of goods. They also explain the differences in pricing and delivery options such as fob and cif terms.