A contract for physical fitness services may contain clauses which:

1. (1) provide for extension of the term of the agreement for a period equal to a period of temporary disability or pregnancy of the customer, or for any other just or reasonable cause;
2. (2) specify that the written contract constitutes the entire agreement between the parties;
3. (3) provide for a renewal option, which to be enforceable must be exercised by the buyer in writing, or by payment by the buyer of part or all of the renewal price. Any renewal option may be exercised only near the expiration of any previous contract and for only twelve months.