Indicate if each of the following descriptions matches messenger RNAs (M), ribosomal RNAs (R), or transfer RNAs (T). Your answer would be a four-letter string composed of letters M, R, and T only, e.g. RRRT.
( ) They contain codons.
( ) They contain anticodons.
( ) They are (covalently) attached to amino acids.
( ) They are at the core of a complex that carries out protein synthesis.