primary efficacy endpoint primary election primary elections primary electrical primary element primary elements primary elevators primary email primary emotion primary emotions primary emphasis primary emulsion primary end point primary endpoint primary endpoints primary enemy primary energy primary energy consumption primary energy demand primary energy production primary energy products primary energy savings primary energy source primary energy sources primary energy supply primary energy use primary engine primary enrolment primary entry primary environmental primary evidence primary example primary examples primary expenditure primary explosive primary export primary factor primary factors primary feature primary features primary field primary filter primary financial primary flight primary flow primary fluid primary focus primary food primary food source primary forces primary forest primary forests primary form primary forms primary fuel primary function primary functions primary general primary goal primary goals primary government primary grade primary grades primary group primary groups primary growth primary guide primary health primary health care primary health care services primary health center primary health centre primary health centres primary health services primary health-care primary healthcare primary heat primary home primary host primary hub primary human primary hydroxyl groups primary hyperhidrosis primary hyperparathyroidism primary hypertension primary identity primary image primary immune primary immunization primary immunodeficiency primary importance primary income primary income account primary incomes primary indicator primary indicators primary industries primary industry primary infection