Mobiles can be the reason a)toothache b)stomachache c)cancer d)headache

C) cancer

D) headache тоже будет верным.

Dear sirs!
Thank You for your letter of April 25 with a request for more information concerning the touch switches, and also to make an offer on this item.
We once again draw your attention to the fact that our products are excellent/high quality and have a number of advantages over similar products in the world market. Our switches are in great demand, so our assigned prices are slightly higher than our competitors.
The switches can be delivered within 2-3 weeks of receiving your order, but the delivery time will largely depend on the quantity of the goods you have ordered.
Our terms of payment: by bill of exchange with payment 30 days after presentation.
With respect,

Dear sirs!
Thank You for your letter of April 25 with a request for more information concerning the touch switches, and also to make an offer on this item.
We once again draw your attention to the fact that our products are excellent/high quality and have a number of advantages over similar products in the world market. Our switches are in great demand, so our assigned prices are slightly higher than our competitors.
The switches can be delivered within 2-3 weeks of receiving your order, but the delivery time will largely depend on the quantity of the goods you have ordered.
Our terms of payment: by bill of exchange with payment 30 days after presentation.
With respect,