Sentence:  There are authorized to be appropriated such sums , to remain available until expended , as may be <WSD>necessary</WSD> , but not more than $ 75000000 in all , ( a ) to carry out the provisions of this Act during the fiscal years 1962 to 1967 , inclusive ; ( b ) to finance , for not more than two years beyond the end of said period , such grants , contracts , cooperative agreements , and studies as may theretofore have been undertaken pursuant to this Act ; and ( c ) to finance , for not more than three years beyond the end of said period , such activities as are required to correlate , coordinate , and round out the results of studies and research undertaken pursuant to this Act : Provided , That funds available in any one year for research and development may , subject to the approval of the Secretary of State to assure that such activities are consistent with the foreign policy objectives of the United States , be expended in cooperation with public or private agencies in foreign countries in the development of processes useful to the program in the United States : And provided further , That every such contract or agreement made with any public or private agency in a foreign country shall contain provisions effective to insure that the results or information developed in connection therewith shall be available without cost to the United States for the use of the United States throughout the world and for the use of the general public within the United States . 
Meaning of the word marked with <WSD> tags:  absolutely essential